The United States last night refused to rule out possible military action against Syria but said it had not exhausted diplomatic moves to get Damascus to change its ways over Iraq and Lebanon.
Addressing the Senate Foreign Relations Committee, Secretary of State Condoleezza Rice said both Syria and Iran were allowing fighters and military assistance to reach insurgents in Iraq.
"Syria and Iran must decide whether they wish to side with the cause of war or with the cause of peace," Ms Rice told a hearing called to discuss US strategy in Iraq, where more than 150,000 US troops are struggling to end an insurgency.
Pressed by senators over whether the Bush administration was planning military action against Syria in particular, Ms Rice said the United States was still on a "diplomatic course" with Damascus but the military option remained open.
"The president never takes any option off the table and he shouldn't," said Ms Rice when asked about a military option.
The Bush administration has accused Syria of doing too little to stop foreign fighters from entering neighbouring Iraq.
Syria says the United States has not done enough to secure the border or deliver technical help it has promised.