The U.S. fired four additional Tomahawk missiles at Libya air defense systems Sunday, bringing the grand total to 124, a senior U.S. Defense official tells Fox News.

Each Tomahawk missile costs $600,000, according to the official, bringing the initial costs of the strikes to approximately $71 million.

"This is not a NATO mission," the defense official told Fox News. "Each contributing nation comes to the fight with its own 'caveats.'" Qatar is now sending fighter planes.

Anti-aircraft fire fire erupted in the Libyan capital Sunday night, with volleys of tracer fire arching into the air, marking the start of a second night of allied strikes on the country. The U.S. and it allies continued to fight against targets of Libyan leader Muammar al-Qaddafi, who on Libyan state radio said the raids were "acts of terrorism".

Qaddafi added that all of the country's people were now carrying weapons to defend the nation.

"We will not leave our land and we will liberate it," he said.

He said he has opened up the weapons depots to Libyans, and said everyone is armed with "automatic weapons, mortars, bombs."

"We promise you a long war," he said in the address.

Qaddafi's comments come as Adm. Michael Mullen, chairman of the U.S. Joint Chiefs of Staff, said U.S. and allied forces have effectively established a no-fly zone over Libya in an interview on "Fox News Sunday."

Mullen said the operation has made significant progress.

"We've had a pretty significant impact in this first 24 hours ... I would say the no-fly zone we were tasked to put in place is now in place," Mullen said on "Fox News Sunday."

His Highness El-Sayyid Idris Abdullah Al-Senussi, nephew of His Majesty King Idris of Libya and the son of His Highness El-Sayyid Abdallah Abed Al-Senussi, made a statement exclusively obtained by Fox supporting military action against Qaddafi.

"I strongly support the military actions taken by coalition forces against Muammar al-Qaddafi," Al Senussi said. "I wish to commend the French forces along with the other coalition nations participating in Operation Odyssey Dawn. I also wish to commend the Arab League for their historic resolution condemning Muammar al-Qaddafi and calling for a no-fly zone in Libya that lead to the U.N. adopting resolution 1973."

"On behalf of the Libyan people I remain committed to supporting the provisional government with the goal of achieving a free democracy with open and free elections for all of Libya."

Pentagon officials Sunday were poring over satellite images to ascertain the damage of Saturday's military strikes.

Large explosions were heard in Tripoli, possibly a cruise missile targeting a command and control center, Fox News' Steve Harrigan reported. Anti-aircraft tracer fire from pro-Qaddafi forces was seen in the night sky after an explosion was heard 2 miles from the compound housing the Libyan strongman.

Thousands of regime supporters, meanwhile, packed into the sprawling Bab al-Aziziya military camp in Tripoli where Qaddafi lives to protect against attacks.

A New York Times report said supporters also packed the interior halls of Qaddafi's compound as human shields, offering to protect the leader against bombings.

British forces have launched air attacks on Libya early Sunday, U.K. defense officials said.

NATO's top decision-making body is set to decide whether the alliance will join in on the strikes in Libya. Diplomats said NATO's military planners are due to present final action plans to the North Atlantic Council on Sunday.

Libya's state television claims that 48 people have been killed and 150 were wounded during military attacks. The report could not be independently verified.

Military strikes by the U.S. and its allies against targets in Libya Saturday "severely disabled" Libyan leader Qaddafi's air defenses, a U.S. official confirmed to Fox News.

The official also warns they do not know what Qaddafi will do next following the military strikes.

"It's too soon to predict what he and his ground forces may do in response to today's strikes," the official told Fox News.

Reuters reports that air strikes by Western forces near Misrata have targeted a military airbase where Qaddafi loyalists are based.

British forces have launched air attacks on Libya, U.K. defense officials said. Three RAF Tornado jets have left the U.K., the first of the British strike force tasked with enforcing a no-fly zone over the country, Sky News reported.

Despite the blow, Qaddafi remained defiant as he threatened to attack military and civilian targets in the Mediterranean in retaliation of international coalition strikes on Libya.

"It is now necessary to open the stores and arm all the masses with all types of weapons to defend the independence, unity and honor of Libya," Qaddafi said in a speech broadcast on Libya state television, according to Reuters. He also warns that weapons depots are being opened to arm the Libyan people in defense.

The Pentagon says 114 Tomahawk cruise missiles have been launched from U.S. and British ships in the Mediterranean, hitting more than 20 Libyan targets along the Mediterranean coastline.

Navy Vice Adm. William E. Gortney, director of the Pentagon's Joint Staff, told reporters the Tomahawk cruise missiles were fired from one British submarine and a number of American destroyers and subs. He said the success of the mission was not immediately clear, adding that additional attacks would commence later.

The U.S. has at least 11 naval vessels in the Mediterranean, including three submarines, two destroyers, two amphibious warfare ships and the USS Mount Whitney, a command-and-control vessel that is the flagship of the Navy's 6th Fleet. Also in the area are Navy P-3 and EP-3 surveillance aircraft, officials said.

The U.S. military strikes clear the way for European and other planes to enforce a no-fly zone designed to ground Qaddafi's air force and cripple his ability to inflict further violence on rebels, U.S. officials said.

President Obama authorized limited military action against Libya Saturday.

"We cannot stand idly by when a tyrant tells his people there will be no mercy," Obama said in a statement from Brazil.

The president also reiterated that the U.S. will not be deploying ground forces into Libya.

A senior military official tells Fox News that the U.S. will be targeting air defenses along the Libyan coast in Operation Odyssey Dawn. There are a total of 25 coalition ships in the Mediterranean, with the U.S. contributing 11 warships.

"Some of the key first strikes that we are planning to strike of course would be on the coast because that where the integrated and missile defense systems are and of course the other air defense related facilities that we will be going after. That would open up the environment where we could enforce the no fly zone throughout from east to west of Libya."

"The U.S. will be at the front end of this," the official told Fox News.

A U.S. defense official also said three B-2 stealth bombers flew non-stop from Missouri and dropped 40 bombs on a major Libyan airfield Saturday night in an attempt to destroy much of Qaddafi's air force.

Officials added that U.S. Air Force fighter jets and U.S. Marine Corps Harrier jump jets also participated.

French fighter jets fired the first shots at Qaddafi's troops, launching the broadest international military effort since the Iraq war in support of an uprising that had seemed on the verge of defeat. The French military says warplanes have carried out four air strikes, destroying several armored vehicles of pro-Qaddafi forces, according to AFP.

Libyan state television is reporting that "crusader enemies" have bombarded civilian targets in Tripoli, Benghazi, and Misrata, according to Reuters.

In the hours before the no-fly zone over Libya went into effect, Qaddafi sent warplanes, tanks and troops into Benghazi, the rebel capital and first city to fall to the rebellion that began Feb. 15.

In an open letter, Qaddafi warned: "You will regret it if you dare to intervene in our country."

Saturday's emergency meeting involved 22 leaders and top officials, including Arab League Secretary-General Amr Moussa and U.N. Secretary-General Ban Ki-Moon and the foreign ministers of Jordan, Morocco and the United Arab Emirates. It was the largest international military action since the beginning of the Iraq war, launched almost exactly eight years ago.

Earlier Saturday, a plane was shot down over the outskirts of Benghazi, sending up a massive black cloud of smoke. An Associated Press reporter saw the plane go down in flames and heard the sound of artillery and crackling gunfire.

Before the plane went down, journalists heard what appeared to be air strikes from it. Rebels cheered and celebrated at the crash, though the government denied a plane had gone down -- or that any towns were shelled on Saturday.

The fighting galvanized the people of Benghazi, with young men collecting bottles to make gasoline bombs. Some residents dragged bed frames and metal scraps into the streets to make roadblocks.

"This city is a symbol of the revolution, it's where it started and where it will end if this city falls," said Gheriani.

At a news conference in the capital, Tripoli, the government spokesman read letters from Qaddafi to Obama and others involved in the international effort.

"Libya is not yours. Libya is for the Libyans. The Security Council resolution is invalid," he said in the letter to Sarkozy, British Prime Minister David Cameron, and U.N. Secretary-General Ban Ki-Moon.

To Obama, the Libyan leader was slightly more conciliatory: "If you had found them taking over American cities with armed force, tell me what you would do."

China expressed "regret" over punishing airstrikes by the U.S. and European nations against Libya to enforce a U.N. no-fly zone.

Foreign Ministry spokeswoman Jiang Yu says China "consistently disagrees with the use of force in international relations" and expressed "regret" over the Saturday attacks. In a statement posted on the ministry's website, Jiang said China "hopes the situation in Libya resumes stability as soon as possible" in order to avoid escalation of a military conflict.

The Associated Press  and NewsCore contributed to this report.