Fares Souaid, the secretary-general of the March 14 coalition, told The Daily Star newspaper in Lebanon it was time for Beirut to get in line behind a Syrian opposition council formed last month in Qatar.
"March 14 will continue to call on the Lebanese government to recognize the new Syrian coalition as the sole legitimate representative of the Syrian people just like Arab countries, the Arab League and most Western countries did," he said.
The Syrian government is under increasing pressure as rebel forces move toward Damascus. British Foreign Secretary William Hague, whose government was one of the first to recognize the opposition council, said support for the opposition is needed to start planning for Syria's peaceful future.
March 14 is led by former Lebanese Prime Minister Saad Hariri. His father, Rafik, was assassinated in a 2005 plot that was said to involve Hezbollah, supporters of the Syrian government. The ruling March 8 coalition in Beirut counts Hezbollah lawmakers among its members.
Members of the opposition Future Movement in Lebanon said they expected to meet formally with members of the Syrian council in the next few days.