Lebanon's anti-Syrian opposition intensified its calls on Wednesday for replacing the government as U.S. warned of a power vacuum in the country.

We don't want to see a vacuum of legitimate political authority that could then be taken advantage of by the Syrians or by others that could create even greater instability and violence,” US Secretary of State Hillary Clinton said after meeting Brazil's foreign minister in Washington.

“We call on all parties in Lebanon to support the process that President Michel Suleiman is leading to choose a responsible, effective, government that can address the threats that Lebanon faces and hold accountable those responsible for last week's bombing,” Clinton said.

Wissam al-Hassan Lebanon's domestic intelligence chief was killed in the capital, Beirut, on Friday in a car bombing, which opposition groups blamed on neighbouring Syria.

His assassination sparked deadly clashes between pro- and anti-Syrian factions in several areas of Lebanon.

?“The current government must leave because the killing machine is part of it, in a direct or indirect way,” Lebanese Christian leader Samir Geagea said.

The Future Current Parliamentary Bloc, led by former Premier Saad Hariri, has called for the formation of a “neutral salvation government” composed of members from outside the rival groups.

?Suleiman had been engaged since on Monday in talks with various political powers in the country to discuss ways and chances of forming a new government to replace the pro-Syrian government of Nagib Mikati.

He had rejected an offer by Mikati to step down, out of fears that the country might plunge into a political vacuum.

Syria's 20-month conflict had polarised Lebanon. The Sunni Muslim community, Lebanon's second largest ethnic group after Shiite Muslims, backed the rebels fighting to overthrow al-Assad.

Many Shiites, including the powerful militant group Hezbollah, backed al-Assad, who belongs to the minority Alawite Shiite sect.?