Tony Snow, the White House spokesman, said on Wednesday that Syria hoped to derail efforts to set up an international tribunal to try those accused of taking part in the 2005 assassination of Rafiq al-Hariri, the former Lebanese prime minister.
"Any such effort to sideline the tribunal will fail, however, for the international community can proceed with establishing it no matter what happens internally in Lebanon," Snow said in a statement.
"The US is committed to working with its international partners and the legitimate government of Lebanon to ensure that the tribunal is quickly established and that all those responsible for the assassinations of Rafiq Hariri and other Lebanese patriots since 2005 are brought to justice.
"Support for a sovereign, democratic and prosperous Lebanon is a key element of US policy in the Middle East.
Rafiq al-Hariri was killed in an explosion in February 2005
"We are therefore increasingly concerned by mounting evidence that the Syrian and Iranian governments, Hezbollah and their Lebanese allies are preparing plans to topple Lebanon's democratically elected government, led by Prime Minister [Fuad] Siniora.
"Any attempt to destabilise Lebanon's democratically elected government through such tactics as manufactured demonstrations and violence, or by physically threatening its leaders, would, at the very least, be a clear violation of Lebanon's sovereignty," he said.
However, on Wednesday, Syria's embassy in Washington said the comments were ludicrous and unfounded.
"What is happening in Lebanon is a purely domestic political issue," the Syrian embassy said in a statement.
"Syria fully respects the sovereignty of Lebanon and does not interfere in its internal politics."
The statement also called on Washington to stop meddling in Lebanese politics and "to stop instigating the Lebanese people against each other and against other countries".
Jumblatt calls for international trial
The US accusation came two days after Walid Jumblatt, the leader of Lebanon's Druze sect, sought US backing for the international court to try suspects in al-Hariri's murder.
Jumblatt said he discussed the proposed tribunal with Condoleezza Rice, the US secretary of state, during an unannounced meeting.
The Druze leader complained of opposition to the court from Emile Lahoud, Lebanon's pro-Syrian president.
"If someone opposes this international court, that means that he is covering up the crime," Jumblatt, a leading anti-Syrian figure in Lebanon's parliament, told reporters after meeting Rice at the US state department on Monday.
"There was a Syrian-Iranian plot to transfer Lebanon into a new Iraq" a key member of the anti-Syrian group, March 14 bloc, told Al Jazeera.