U.S. troops shot back, killing one person and arresting another.
In the troubled city of Fallujah — the scene of almost constant clashes since U.S. troops killed 18 demonstrators in two confrontations in April — another U.S. patrol came under fire.
U.S. Central Command says the soldiers did not return fire but arrested two suspects.
Meanwhile, captured terrorists are casting doubt on another piece of the Bush administration's rationale for war in Iraq: the alleged link between Saddam Hussein and al Qaeda.
In other developments:
Bush administration officials are denying they exaggerated the threat of Iraq's arsenal to justify a war.
Secretary of State Colin Powell says U.S. officials will intensify their search in Iraq. Powell told CNN there's "no doubt" that Iraq had chemical and biological weapons.
As the search for weapons evidence has gone on without success, administration officials have denied that illegal arms was the lead reason for going to war. Baghdad's links to al Qaeda were also important, they say.
But now the New York Times reports two high-ranking members of the terror network who are in U.S. custody have denied that any alliance existed.
Quoting intelligence sources, The Times that al Qaeda planner Abu Zubaydah has told interrogators that Osama bin Laden considered a partnership with Saddam but decided against it. Khalid Shaikh Mohammed, an operations chief, has also denied any connection.
According to the newspaper, Zubaydah told intelligence officers there was no link in interrogations last year, before the U.S. made the push for war against Saddam. The Bush administration has not made either statement public.
Administration officials caution that the captured terrorists could be lying, and say they have found other evidence in Iraq suggesting a link may have existed.
But, as it has on the issue of weapons of mass destruction, critics may focus on the fact that the administration may have made unqualified allegations when the intelligence was murky.
In his State of the Union speech in January, President Bush said: "Evidence from intelligence sources, secret communications, and statements by people now in custody reveal that Saddam Hussein aids and protects terrorists, including members of al Qaeda."
A week later, in his presentation to the Security Council, Powell described "the potentially much more sinister nexus between Iraq and the al Qaeda terrorist network, a nexus that combines classic terrorist organizations and modern methods of murder."
Powell said Iraq "provides haven and active support for terrorists."