Two aides of a Lebanese Druze minister were killed on Sunday when his convoy came under fire in an area that supports a rival faction.
Saleh Al Gharib, Lebanon's Minister of State for Refugee Affairs, is close to pro-Syrian Druze leader Talal Arslan. Mr Al Gharib called the attack an assassination attempt.
The Mount Lebanon town near Aley, where the incident took place, is an area of support for Druze leader Walid Jumblatt, a fierce opponent of the Syrian government and rival to Mr Arslan.
Mr Jumblatt's Popular Progressive Party denied any involvement.
It was "an armed ambush and a clear assassination attempt", Mr Al Gharib told Lebanon's Al Jadeed TV. "There appears to be a decision to blow up the situation on the mountain.
A member of Mr Jumblatt's party was wounded in the incident, the National News Agency reported.
Mr Jumblatt, Lebanon's main Druze leader, and Mr Arslan are historic rivals whose parties vied for posts in the national unity government formed this year.
The tension on Sunday grew after Foreign Minister Gebran Bassil, a Maronite Christian who is a political ally of Mr Arslan, planned to visit the area, which led protesters to block roads.
Mr Bassil cancelled the visit, described as provocative by Mr Jumblatt's party, because of the protests.
Akram Chehayeb, a senior official with the party and Minister of Education, also urged calm.
"What happened is the result of poor judgment by some officials and is a recipe for strife on the Mountain," Mr Chehayeb said.
Prime Minister Saad Al Hariri made contact with the Druze parties, security chiefs and Mr Bassil "on the need to ease tension in Aley and to exert all efforts to calm the situation", his office said.
The army had sent a large number of troops to the area, Defence Minister Elias Bou Saab told broadcaster LBC.
President Michel Aoun has called a meeting of Lebanese security chiefs on Monday, his office said.
Mr Arslan's supporters blocked a main highway south with burning tyres, choking traffic for hours.