The Security Council has also approved plans for a special international tribunal to try suspects in the 2005 killing of former Lebanese Prime Minister Rafik Hariri.
Gemayel's killing comes amid a political crisis in Lebanon, following the resignation of six pro-Syrian cabinet members.
Lebanese President Emile Lahoud vowed Gemayel's killers would be punished.
"We will not allow this terrorist act to go unpunished," Lahoud said. "We will do anything to find the perpetrators because, I assure you, those criminals are against all Lebanese people and, in this sense, I would like to reiterate that our unity is our strength. The only way to get to the bottom of this conspiracy is to work together and find all solutions to all our problems as soon as possible."
U.S. President George W. Bush called for a full investigation. Those condemning Gemayel's killing included France, Britain, Russia, Iran, and Syria, which rejected suggestions it may have been behind it.
(Reuters, AP, AFP)