US President George W Bush says he has long since lost patience with Syria's President Bashar al-Assad, and has ruled out opening a dialogue with him.
While the US accuses Syria, Syria accuses the US
"He doesn't need a phone call, he knows exactly what my position is," Mr Bush said at a year-ending news conference.
The US and Syria have each accused the other of meddling in Lebanon, where repeated attempts to find a new president have failed.
Mr Bush also accused Mr Assad of supporting militant groups.
"My patience ran out on President Assad a long time ago," Mr Bush told reporters at the White House.
"The reason why is because he houses Hamas, he facilitates Hezbollah, suiciders go from his country into Iraq, and he destabilises Lebanon."
Lebanon has had no president for nearly a month since Emile Lahoud left office, and many parliamentary sessions called to elect one have been cancelled.
The pro-Western ruling bloc and pro-Syrian opposition have agreed on a presidential candidate, army chief General Michel Suleiman, but are divided on the make-up of the new government.
The deadlock over the president is Lebanon's worst political crisis since the country's long civil war ended in 1990.
Syria's Foreign Minister, Walid Muallem, on Thursday accused the US of blocking attempts to broker a deal.
"The American role has held up the French-Syrian efforts towards a solution," he said.
He accused the US of trying to sideline the Syrian-backed opposition, saying it wanted the Western-backed majority "to monopolise political decisions in Lebanon".
During his news conference at the White House Mr Bush also touched on a wide range of other issues.
He said he believed a Republican would win the US election next year, that he would consider all options to stimulate the US economy, and criticised the number of "wasteful" local projects in the US budget as passed by Congress.
He also said his administration was "developing a strategy" that "will deal" with global warming.