Many Syrian nationals were killed in fighting overnight in the Iraqi capital and others have been taken prisoner, said US Defense Secretary Donald Rumsfeld, who said Syrians had entered Iraq by the busload.

"The Syrian government needs to cooperate with the United States and our coalition partners. It must not harbor any Baathists, any military officials who need to be held to account for their tenure" in Iraq, President George W. Bush told reporters at the White House.

Bush stopped short of threatening US action against Damascus, but his comments were the latest warning to Syria to halt support for the deposed Iraqi regime and its leaders.

"We expect them to do everything they can to prevent people who should be held to account from escaping in their country," he said.

"And if they are in their country, we expect the Syrian authorities to turn them over to the proper folks," said Bush.

"We believe there are chemical weapons in Syria," Bush said without elaborating.

US intelligence has previously reported that Syria possesses stockpiles of the nerve gas sarin and is believed to have an active biological program.

Rumsfeld said earlier that the United States had reports that some of Iraq's weapons of mass destruction may have been sent to a neighboring country, but would not identify the country.

"Each situation will require a different response," Bush said. "First thing's first. We're here in Iraq now."

In an interview with the BBC, Secretary of State Colin Powell warned Damascus it would be "very unwise if, suddenly, Syria becomes a haven for all these people who should be brought to justice, who are trying to get out of Baghdad."

"The government's making a lot of bad mistakes, a lot of bad judgment calls, in my view, and they're associating with the wrong people," Rumsfeld said in a interview here with CBS television.

Syrian officials emphatically denied that it was harboring members of the regime or had weapons of mass destruction, and said Washington was seeking to divert attention from the chaos and lawlessness that has followed the collapse of the Iraqi regime.

"We will not only accept the most rigid inspection regime, we will welcome it heartily," said Imad Moustapha, the number two in the Syrian embassy in the United States.

Rumsfeld declined to comment on a report in the Washington Times that two top Iraqi scientists involved in its weapons of mass destruction program had taken refuge in Syria.

Asked what if Iraqi President Saddam Hussein turned up alive in Syria, Rumsfeld said, "Then I think Syria would have made an even bigger mistake."

Saddam heads a US list of more than 50 Iraqis wanted by coalition forces.

Targeted in at least two "decapitation" air strikes during the 23-day-old war, his fate remains a mystery.

US Army General Tommy Franks, the commander of the coalition forces, said US forces have samples of Saddam's DNA.

He told CNN he believed it would be possible to identify Saddam, "unless remains were removed" at the site of recent heavy bombings in a residential area where Saddam was believed to be meeting with his top intelligence officials.

Rumsfeld said that if the Iraqi leader is alive, he might try to escape the country.

Bringing in Iraqi leaders and scientists has become a top priority for US forces as they turn their attention from combat to uncovering Iraq's hidden weapons of mass destruction programs.

"We're not going to find anything until we find people who tell us where the things are," Rumsfeld said. "And when we do, then we'll learn precisely where things were and what was done."

Contrary to US expectations, Iraqi forces used no chemical or biological weapons in the war, and so far none have been found.

At least one senior figure in the Iraqi nuclear program was in US custody, Rumsfeld said.

Franks said some Iraqi leaders were seized trying to escape the country and were in US custody in western Iraq.

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