Mr Feltman (right) held talks with Lebanese President Michel Suleiman
Two senior US envoys have reassured Lebanon that America's recent moves towards improving relations with Syria will not be at Beirut's expense.
The comments by Jeffrey Feltman and Daniel Shapiro came after their talks with top Lebanese leaders in Beirut.
The two envoys are due to travel to neighbouring Syria on Saturday.
Some Lebanese pro-Western politicians fear Washington's overtures to Syria - Lebanon's long-dominant neighbour - may weaken America's support for Beirut.
Last year, the Western-backed parliamentary majority opposed to Syrian influence in Lebanon and a coalition led by Hezbollah signed a deal to calm a long-running power struggle in Lebanon.
Syria pulled out its troops from Lebanon in 2005, ending a 29-year presence in the country.
The move came soon after Lebanese former Prime Minister Rafik Hariri was killed in a car bombing in Beirut.
Damascus has denied accusations that it was involved in the attack.
"My visit here today underscores an important reality - the United States' support for a sovereign and independent Lebanon remains unwavering," Mr Feltman, the former US ambassador to Lebanon, said after the talks in Beirut.
"The president [Barack Obama] has said he wants to sustain in principle engagement with all states in the region and that includes Syria," he said.
However, Mr Feltman said he and Mr Shapiro, a White House official, planned to discuss a "long list" of concerns during their talks in Syria over the weekend.
"Our trip to Syria... is an opportunity for us to start addressing these concerns and using engagement as a tool to promote our objectives in the region," Mr Feltman said.
The talks in Damascus are seen as the strongest indication so far of the Obama administration's willingness to engage with Syria, which former President George W Bush had sought to isolate.