The United States has no credible evidence that Iraq moved weapons of mass destruction (search) into Syria early last year before the U.S.-led war that drove Saddam Hussein from power, National Security Adviser Condoleezza Rice said Friday.

Rice said, "Any indication that something like that happened would be a very serious matter.

"But I want to be very clear: we don't, at this point, have any indications that I would consider credible and firm that that has taken place, but we will tie down every lead," she said at a White House briefing about Bush's trip Monday to a hemispheric summit in Mexico.

In nine months, arms control experts in Iraq have failed to find a single item from a long list of weapons of mass destruction. The Bush administration cited an alleged weapons stockpile in Iraq as a primary reason for launching the war against Saddam's government.

"We're going to follow every lead on what may have happened here," Rice said. "I don't think we are at the point that we can make a judgment on this issue. There hasn't been any hard evidence that such a thing happened.

"But obviously we're going to follow up every lead," she said, "and it would be a serious problem if that, in fact, did happen."

Rice said the United States talks with Syria about a number of issues, "including the borders with Iraq and what may have happened in the past there and what may be continuing to happen there." Mainly, she said, the United States opposes Syria's support for terrorism, particularly its support for anti-Palestinian groups Hezbollah (search) and Hamas (search).