Officials said that despite numerous appeals, Syria has failed to stop the flow of Sunni suicide bombers to Iraq. They said the lion's share of suicide bombers were foreign Arab nationals who entered Syria and made their way to Iraq.

"They [suicide bombers] see Syria as a more accommodating country through which to transit across the border to come into Iraq to perpetrate their terror," Satterfield.

Satterfield said the U.S. intelligence community has assessed that between 85 and 90 percent of suicide bombers in Iraq entered from Syria. In an address to the Washington Institute on March 27, Satterfield said 90 percent of suicide bombers in Iraq were foreigners.

In his address, Satterfield again warned Syria to stop the flow of would-be suicide bombers and other insurgents to Iraq. He said Iraq and the United States have sought to stem the flow of insurgents from Syria to Iraq's Al Anbar province.

"It has to stop," Satterfield said. "It is not in Syria's long term interests to let this violence continue. We and the Iraqi security forces have done our best. It is a long, long border."

Over the last month, the Bush administration has resumed high-level contacts with the Syrian regime of President Bashar Assad. Officials said that during the March 10 meeting in Baghdad, the U.S. delegation accused Iran and Syria of interfering in Iraq. Secretary of State Condoleezza Rice was expected to attend the next meeting that included Syria in April.

"We would hope that the Syrian government understands as well that its rhetoric for a peaceful and stable Iraq has to be matched by actions," Satterfield said.

In Iraq, foreign suicide bombers coming from Syria have increasingly used chlorine in their attacks. On Wednesday, at least 15 Iraqi and U.S. soldiers were injured when suicide bombers detonated explosives on trucks that contained chlorine in the Anbar province.