The United States has stepped up its criticism of Syria, accusing Damascus of having chemical weapons and allowing senior Iraqi leaders to escape through its territory.Syrian nationals battled US invasion troops in Baghdad after entering Iraq by the busload, Defense Secretary Donald Rumsfeld said Sunday. Many Syrian nationals were killed in fighting overnight in the Iraqi capital and others have been taken prisoner, Rumsfeld said. "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. .

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

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.

"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.

And 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."

Syrian officials emphatically denied that it was harboring members of the regime or had weapons of mass destruction, andsaid.

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 (weapons) inspection regime, we will welcome it heartily," said Imad Moustapha, the number two in the Syrian embassy in the United States.

A half brother of Saddam, Watban Ibrahim Hasan, was captured near the border with Syria trying to flee the country, a US official confirmed.

US invasion Army General Tommy Franks said foreigners were fighting as paid mercenaries in Iraq.

He said mercenaries were "from a number of countries. Syria as well as a number of others... They have come in as mercenaries been paid by the Iraqis."

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

PHOTO CAPTION

Arab volunteers to fight for Iraq display their weapons at a camp just outside Baghdad. People from several different countries volunteered to come to Iraq to fight against the US-led coalition(AFP/File/Karim Sahib)