U.S. Navy pilots resumed strikes against Taliban and Al Qaeda targets early Monday, focusing increasingly on mobile targets, as the Pentagon pressed its bombing and covert special forces ground campaign.

Secret missions by special operations forces were continuing on the ground, two defense officials said on condition of anonymity. They gave no details.

U.S. warplanes opened a third week of airstrikes Sunday, hitting north of the Afghan capital of Kabul.

The bombardment of Taliban positions near a front line north of Kabul marked what could be the start of a more aggressive campaign on behalf of opposition forces fighting the Islamic regime.

The attacks Sunday were the closest and most intense strikes so far against Taliban positions defending Kabul from Northern Alliance forces. Alliance officials had been asking the United States to bomb the front line north of Kabul so that they could advance on the capital, but until now U.S. bombing of front line positions has mostly taken place around the strategic northern city of Mazar-e-Sharif.

Afghan officials also reported air attacks Sunday around the western city of Herat, Kandahar in the south and the front line positions near Mazar-e-Sharif.

Secretary of State Colin Powell said the United States was "very interested " in seeing rebel forces take Mazar-e-Sharif, but was still "continuing discussion" about whether a rebel march into Kabul would be "the best thing."

The United States and Britain had been reluctant to help the alliance seize Kabul until a broad-based government had been formed to take over from the Taliban.

Asked whether U.S. forces would kill Usama bin Laden on sight, Gen. Richard B. Myers, chairman of the Joint Chiefs of Staff, said it depends on what happens when he's found.

"If it's a defensive situation, then bullets will fly, but if we can capture somebody, then we'll do that," he said on ABC's This Week.

Asked the same question, Powell told CNN's Late Edition: "Our mission is to bring him to justice or bring justice to him."

President Bush signed an order last month directing the CIA to destroy bin Laden and his communications, security apparatus and infrastructure in retaliation for the Sept. 11 World Trade Center and Pentagon attacks, a senior administration official said Sunday.

Bush also added more than $1 billion to the spy agency's war on terrorism, most of it for the new covert action.

The U.S.-led military campaign already has crippled terrorists' bases and their ability to train in Afghanistan, Myers said.

"They won't be doing any training in the near future in Afghanistan," he said.

Myers said the fight against the ruling Taliban regime and bin Laden's Al Qaeda terrorist network is "a war we must win if we want to maintain our freedom."

The aerial bombing began Oct. 7, followed by the first publicly acknowledged ground assaults Saturday.

In lightning strikes under cover of darkness, 100 airborne Army Rangers and other special forces hit a Taliban-controlled airfield and a residence of Taliban leader Mullah Mohammed Omar near the southern city of Kandahar. They destroyed a cache of weapons, killed an undetermined number of Taliban forces and accomplished their objectives, the Pentagon said.

They also left behind a message — copies of a photo of firemen raising the American flag on the rubble of the World Trade Center superimposed with the words "Freedom Endures," a Pentagon official said.

"They had two objectives, one was the Taliban leadership compound, especially Omar's compound, the other was an air field," Myers said Sunday. "On both of them we thought there was a pretty good chance we could find some useful intelligence."

Documents and other items taken during the assaults were being analyzed Sunday for their intelligence value, defense officials said.

As has been the Pentagon's practice, Myers would not describe the continuing missions, citing safety concerns for troops.

"I doubt if a coach is going to give away his game plan for today before he executes that plan," he said.

But two defense officials, speaking on condition of anonymity, said Sunday that forces were pressing on with a wide range of operations, including some meant to be kept secret even after they are over.

Myers denied the Taliban's claim that it shot down a U.S. helicopter, killing 20 to 25 American soldiers. He also said he had no information on reports that at least one U.S. soldier was injured by a land mine and several soldiers may be missing.

The Pentagon has said two Rangers were killed in Pakistan when a Black Hawk helicopter crashed during poor visibility.

Officials said Sunday that hostile fire had been ruled out as a cause of the accident, which they were still investigating. They identified the Rangers as Spc. Jonn J. Edmunds, 20 of Cheyenne, Wyo., and Pfc. Kristofor T. Stonesifer, 28, of Missoula, Mont. They served with the 75th Ranger Regiment based at Fort Benning, Ga., the Army said.

Officials would not disclose the role of the Black Hawk, although some believed it was preparing to swoop across the border into Afghanistan in the event any Rangers had to be rescued.

Meantime, Powell reiterated there is no timetable for completion of military operations. However, he said the onset of winter and the start of the Muslim holy month of Ramadan — both arriving in mid-November — could have an impact on how they are conducted.

Also Sunday, the British Broadcasting Corp. quoted an Afghan doctor as saying the 10-year-old son of Taliban leader Omar was killed during U.S.-led strikes. The boy died two weeks ago, on the first night of bombing raids on the Taliban stronghold of Kandahar, Dr. Abdul Barri said.

The Associated Press contributed to this report.