The UN is stepping up efforts to end the deadlock over how to try those suspected of killing former Lebanese Prime Minister Rafik Hariri.
The Hariri killing sparked protests that forced Syria out of Lebanon
UN Secretary General Ban Ki-moon is sending his top legal adviser to the country next week.
Mr Hariri and 22 others were killed in a massive bomb explosion in Beirut on 14 February 2005.
Lebanon's current prime minister, Fouad Siniora, backs plans for an international tribunal.
The mainly pro-Syrian opposition has reservations about the tribunal and is accused by the government of trying to undermine it.
Nicholas Michel, the UN's top legal adviser, will visit Lebanon on Tuesday to try to help the rival parties find common ground over proposals to set up an international tribunal.
"We simply want to make sure that everybody has an opportunity to share his or her proposals, and make sure that at the end we have a broad support in the country for the establishment of the tribunal," he said.
The UN says Mr Hariri's killing was "probably" politically motivated and has implicated Syria but Damascus has denied any involvement in his death.
The UN has signed an accord that would create an international tribunal but the move has been opposed by Syria and Lebanese President Emile Lahoud.
Syrian President Bashar al-Assad has said any Syrian suspects would be tried in Syria and he would not release them to a tribunal.
If Lebanon fails to ratify the proposal, the Security Council may consider independently authorising a tribunal as it did in Rwanda and the former Yugoslavia.
Saad Hariri, Rafik Hariri's son, has urged the UN Security Council to bypass the political parties and establish a tribunal, if the Lebanese parties cannot agree.