President Bush has urged Syria to "immediately free all political prisoners" and stop what he called "efforts to undermine Lebanese sovereignty."
Mr. Bush said in a statement Wednesday that he is troubled by reports some ailing political prisoners in Syria are denied health care, while others are held with violent criminals.
The president also accused Syria of "denying the Lebanese people their right to participate in the democratic process," free of foreign interference.
Syria supports the Shi'ite militant group Hezbollah, which has been demanding that the Western-backed Lebanese government resign.
A U.S. senator, meanwhile, met with Syrian President Bashar Assad today in Damascus. Bill Nelson, a Democrat from Florida told reporters he saw an opening for dialogue between the U.S. and Syria.
White House spokesman Tony Snow said the meeting was not appropriate.
Nelson said Mr. Assad expressed a willingness to cooperate in stabilizing Iraq.
The U.S. State Department had tried to discourage Nelson from making the trip.
A bipartisan U.S. panel - the Iraq Study Group - recommended last week that the Bush administration consider talks with Iran and Syria on improving security in Iraq. The White House has been cool to the idea.