The UN Security Council has narrowly adopted a resolution demanding that foreign troops leave Lebanon and that Lebanese sovereignty be respected.
Correspondents say Emile Lahoud is Syria's strongest ally in Lebanon
The resolution is aimed at Syria, which has troops in the country and strongly backs Lebanese President Emile Lahoud, a close ally of Damascus.
The Beirut parliament is due to vote on a plan to change the constitution and allow Mr Lahoud a second term.
A Syrian official dismissed the Security Council resolution.
Foreign Ministry spokeswoman Bushra Kanafani said the United States had failed to get the resolution it wanted through the council.
"The resolution that was adopted lacks the main points that the draft had sought against Syria and does not call for Syria to withdraw from Lebanon," Mc Kanafani said.
The US and French-backed resolution won nine votes, the minimum needed to pass.
The other six members of the Security Council abstained - including China and Russia, two permanent members with veto power.
The resolution declared "support for a free and fair electoral process in Lebanon's upcoming presidential election, conducted according to Lebanese constitutional rules devised without foreign interference or influence".
It also called on all parties concerned to work for "the restoration of the territorial integrity, full sovereignty, and political independence of Lebanon".
BBC United Nations correspondent Stephen Gibbs says the resolution is couched in diplomatic language and does not mention Syria directly by name, but it is squarely aimed at Damascus and its involvement in the affairs of Lebanon.
The resolution was amended to ensure it would pass. A demand "that Syrian forces withdraw without delay from Lebanon" was changed to demand "that foreign forces withdraw without delay from Lebanon".
US ambassador John Danforth told the council: "We believe Lebanon should be allowed to determine its own future and assume control of its own territory.
Syrian forces have been in Lebanon since 1976
"Yet the Lebanese people are still unable to exercise their rights as a free people to make those choices and to take those steps as a nation."
A senior Lebanese official had asked council members to withdraw the resolution, saying the body had never interfered in this manner in the internal affairs of a member-state.
Mohammed Issa, Lebanon's secretary-general for foreign affairs, said Syrian troops were in the country at his government's request to help rebuff "radical action emanating from Israel".
Mr Lahoud is Syria's strongest ally in Lebanon, where about 17,000 Syrian troops are still stationed.
Syria has been pushing for an extension of the mandate of Mr Lahoud, whose six-year term ends in November. The country's constitution forbids presidents from seeking re-election.
BBC Beirut correspondent Kim Ghattas says many Lebanese politicians are opposed to the extension of Mr Lahoud's term.
They say the decision was made in Damascus and imposed on top Lebanese officials.
Syria's involvement in Lebanon dates back to 1976, when it sent troops into Lebanon to try to quell a year-long civil war. The conflict raged on for another 14 years.
But the troops have remained and Damascus' military and political influence in Lebanon remains strong. Syria is believed to be the main backer of Hezbollah.
Damascus argues that its troop presence in Lebanon is a stabilising influence.