US Senate Intelligence Committee chairman Mr Pat Roberts says there is some concern Iraqi weapons of mass destruction have gone to Syria, as Washington vowed to carry on searching for such arms in Iraq.
Mr Roberts, a leading member of President George W. Bush's Republican party, said: "I think that there is some concern that shipments of WMD (weapons of mass destruction) went to Syria." He did not elaborate.
Syria, which borders Iraq, has in the past denied US charges it has weapons of mass destruction programmes and supports "terrorist activity".
"The jury is still out," US Vice President Dick Cheney said on the failure so far to find any weapons of mass destruction since Saddam was toppled last April.
"It's going to take some additional considerable period of time to look at all of the cubby holes and...dumps and all the places in Iraq where you might expect to find something like that," Mr Cheney told US National Public Radio.
Mr Cheney begins a five-day trip to Europe today designed to mend fences after bitter divisions in the international community over the Iraq war.
He will join business and political leaders at the World Economic Forum in Davos, Switzerland on Saturday and seek other countries' help in rebuilding Iraq.