BAGHDAD - The United States said an al Qaeda operative was plotting to provoke a civil war in Iraq as UN Secretary-General Kofi Annan expressed concern over divisions among Iraqis on a plan to assume power.

US officials in Baghdad said US forces had seized a computer disc that contained a letter outlining the plan written by Abu Musab Zarqawi, who Washington suspects of links to Ansar al-Islam - a Muslim militant group operating in Iraq.

"There is clearly a plan on the part of outsiders to come into this country and spark civil war, breed sectarian violence and try to expose fissures in the society," Brigadier-General Mark Kimmitt, the top US military spokesman in Iraq, said.

"We believe the document is credible and we take the threat seriously."

Dan Senor, chief spokesman for Iraq's US governor Paul Bremer, said the 17-page letter proposed attacks on the shrines and leadership of Iraq's Shi'ite Muslim majority, whom Arab Sunnis and Kurds fear could dominate a future government.

"The document... talks about a strategy of provoking violence targeted at the Shia, the Shia leaders in the hope that it would provoke reprisals against other ethnic groups in the country," he said.

In Washington, Secretary of State Colin Powell said the letter al Qaeda was under pressure, but had not given up.

"With respect to the letter itself, it's very revealing. They describe the weaknesses they have in their efforts to undercut the coalition's effort," Powell said.

"But at the same time, it shows they haven't given up. They're trying to get more terrorists into Iraq... But they will not succeed."

Iraq's US occupiers have long said they suspect al Qaeda has played a role in the insurgency against US troops and particularly in attacks on civilian targets in Iraq.

In October, Washington offered a reward of up to US$5 million for information leading to the arrest or conviction of Zarqawi.

He is also suspected of orchestrating the murder of US diplomat Laurence Foley in the Jordanian capital in 2002. Zarqawi was sentenced to death in absentia by a Jordanian court last year for plotting attacks against US and Israeli targets.

In New York, Annan spoke to UN Security Council members about the electoral team he sent to Baghdad on Saturday to see whether elections could be held quickly, as Shi'ites want, or recommend alternatives for selecting Iraqi leaders before the United States relinquishes power on June 30.

"I am concerned that there is no consensus yet on the best way to handle the transition," Annan said, according to his speaking notes. "Many Iraqis have been calling for elections before June 30. Others disagree and prefer other options for choosing the members of Iraq transitional institutions."

US President George W. Bush wants UN help to arrange an early transfer of sovereignty to Iraqis, an effort to ease the postwar violence in the country and dispel concerns of extended US rule as he faces a tough re-election fight in November. (Agencies via Xinhua)