One of the world's most sought after and dangerous terrorists thought to be coordinating attacks in Iraq is likely basing his operations in Fallujah (search), senior defense officials have told Fox News.

They said the details on Abu Musab al-Zarqawi's (search) likely whereabouts came from the interrogation of Umar Baziyani (search), an associate of al-Zarqawi that was apprehended by Iraqi police forces on June 4.

Baziyani told interrogators that al-Zarqawi "has been and is still operating out of Fallujah."

More interrogation revealed Zarqawi's plans to ramp up violence and attacks on coalition forces leading up to the June 30 handover of power to Iraqis.

Considered the most dangerous foreign fighter in Iraq, al-Zarqawi now is believed to have connections to radicals around the globe — including the United States — and has firmly secured his position among the government's most wanted terrorists.

With al-Zarqawi's public profile in the terror world growing, U.S. officials say he's joined the club of leading terrorists that includes Usama bin Laden (search), his deputy Ayman al-Zawahri (search) and few, if any, others.

During al-Zarqawi's years of experience fighting for jihadist causes, the officials say he has developed ties to terror plotters and other Muslim extremists, including individuals in the United States who sympathize with his violent agenda.

The officials declined to offer specifics and spoke on the condition of anonymity because of the sensitive nature of the subject.

Attention on al-Zarqawi has increased in recent months as he became a more vocal terror figure, due in part to three recordings released on the Internet, including that of the beheading of American businessman Nicholas Berg (search).

Even this winter, such a profile was uncharacteristic of the 36-year-old al-Zarqawi, a Jordanian previously not known for claiming responsibility for the numerous attacks in which he's believed to have had a hand.

Thought of as an ally rather than a member of Al Qaeda, al-Zarqawi is not believed to have direct command-and-control links to Al Qaeda operatives thought to be in the United States, said an FBI official, speaking on condition of anonymity, citing bureau policy restraining public comments on sensitive investigations.

But it is likely, the FBI and other U.S. officials said, that some of these operatives were associated with him at different times.

Interest in capturing or killing al-Zarqawi is increasing. While officials have said the terror plotter is believed to be in Iraq, they won't say where. Indications are that U.S. forces are moving into the Fallujah-Ramadi area to track him down.

The State Department and other agencies that handle counterterrorism are considering raising the reward for information leading to his killing or capture from $10 million to $25 million, putting him on par with bin Laden, al-Zawahri and jailed Iraqi President Saddam Hussein.

Last week, U.S. aircraft over Iraq were dropping leaflets reminding people of the reward.

Intelligence officials believe al-Zarqawi has cells or links to Muslim extremists around the world, including countries he has been known to have spent time in: Iraq, Afghanistan, Turkey, Spain, Saudi Arabia, Sudan, Syria, Pakistan and Kuwait.

Secretary of State Colin Powell has also said that al-Zarqawi and his network have plotted against countries including France, Britain, Italy, Germany and Russia.

Al-Zarqawi, whose real name is Ahmad Fadhil al-Khalayleh, joined the jihadist cause in his teens, traveling to Afghanistan to fight alongside the mujahadeen, or holy warriors, trying to prevent a Soviet occupation. The street-smart plotter is thought to have become a student of Islamic literature.

He was known as the "one-legged terrorist" because U.S. intelligence indicated he received medical treatment and was fitted with an artificial leg in Baghdad in 2002, after fleeing Afghanistan.

However, the view now is that al-Zarqawi has both legs, even though he is still believed to have traveled to Iraq for treatment for his leg or another injury, a U.S. intelligence official said, speaking on the condition of anonymity.

Al-Zarqawi has been blamed for having a hand in dozens of attacks worldwide. In a letter intercepted in January, al-Zarqawi took credit for 25 attacks alone in Iraq.

On Tuesday, a group claiming to be led by al-Zarqawi — the Monotheism and Jihad (search) group — took responsibility for a car bomb attack on a convoy in Baghdad that killed 13, including three General Electric Co. employees.

Last week, the group also claimed responsibility for deadly attacks outside a U.S. military base in Iraq and an ambush that killed four employees of an American security company. U.S. officials are still looking into the claims.

Al-Zarqawi is also blamed for the bombings of the U.N. headquarters in Baghdad in August, a mosque in Najaf, also in August, and the Italian police headquarters in November.

He was convicted of orchestrating the assassination of U.S. aid worker Laurence Foley in Amman in 2002, and was sentenced to death in absentia.

Fox News' Bret Baier and the Associated Press contributed to this report.