US Assistant Secretary of State for Near Eastern Affairs William Burns said in Damascus on Saturday: "Syria must end its interference in Lebanese internal affairs, withdraw its forces from Lebanon and allow the Lebanese armed forces and government to establish their authority throughout Lebanon."
He added, "The time has come for concrete steps ... We stress that what is essential now is genuine progress, not rhetoric."
But Burns also held out an olive branch to Damascus, promising that cooperation would be rewarded with relations on a "very different course" than the unilateral sanctions imposed by Washington earlier this year.
"If Syria takes action on these concerns, our relationship can take a very different course with positive results," he said after his talks with top leaders.
Last week the UN Security Council adopted a resolution drafted by the United States and France calling on all foreign forces to leave Lebanon, militias to disband and foreign governments to respect Lebanese sovereignty.
Lebanon's parliament recently
extended Lahud's stay in office
Despite the resolution, Lebanon's parliament changed the constitution to allow Syrian-backed President Emile Lahud to stay in office for three more years.
The resolution does not mention Syria by name, but it is seen as an attempt to stop Damascus's tight control of Lebanese politics and get rid of the 17,000 troops Syria keeps in its smaller neighbour.
Syrian forces entered Lebanon in 1976 at the outset of the country's bloody civil war. Although the country is now at peace Damascus insists that they remain as a defensive measure against arch-foe Israel until a final peace deal is reached.
Lebanon will send a delegation to the Security Council later this month to present Beirut's case. Syria has also rejected the resolution.