The fragile coalition government in Lebanon collapsed after 12 cabinet ministers - mostly from Hizbollah and its allies - resigned on Wednesday.
The BBC reports the crisis was sparked by a dispute over a UN tribunal investigating ex-Prime Minister Rafik Hariri's murder.
President Michel Suleiman has asked prime minister Saad al-Hariri to stay on in a caretaker role.
The Arab League appealed for calm over Lebanon's "tense" security situation.
The BBC reports Hizbollah opposes the tribunal, which is expected to indict several of its members over the 2005 assassination of Rafik Hariri in a massive truck bomb in central Beirut.
The first indictments are expected to be presented next week, although their release has been delayed several times already.
Political parties are now trying to form a new governing coalition.
Mr Hariri - Rafik Hariri's son - was in Washington for a meeting with President Barack Obama when his ministers resigned.
He then moved on to Paris for a meeting with French President Nicolas Sarkozy, but has not publicly commented on developments. He is expected back in Beirut on Thursday.