Lebanon's caretaker prime minister said Thursday he will seek the post again after the militant group Hezbollah toppled his government, escalating fears the country's political crisis could descend into street battles.

Saad Hariri's Western-backed government collapsed last week in a dispute over a U.N. tribunal investigating the assassination of his father, former prime minister Rafik Hariri. Many fear Hezbollah — widely expected to be indicted by the court — will react violently if accused.

Hariri's defiant comments heighten an already tense faceoff with Hezbollah and its allies, who have insisted they will not accept Hariri as a candidate for prime minister again in talks due to start on Monday.

Hariri said Hezbollah's stance torpedoed attempts by Qatar and Turkey to find a compromise to defuse the crisis.

"Their demand that I do not return as prime minister stopped the move toward a solution," said Hariri, 40, speaking in front of a poster of his father, who was killed in a massive truck bombing along Beirut's waterfront in 2005. "Their aim is to sideline me from the political process and assassinate me politically."

Hariri insisted he would continue efforts to solve the crisis diplomatically.

"We will go to the consultations and we will give our opinion while committed to my nomination for the prime minister's post," he said.

Hariri also appealed for calm, saying: "Any drop of blood that falls from any Lebanese citizen is more important to me than any post."

Lebanese special police forces tightened security around the government palace and other official buildings Thursday amid growing fears that the country was headed toward violence.

A senior security official confirmed to The Associated Press that the security measures in and around Beirut stem from "concerns of movements on the ground by some parties." The official spoke on condition of anonymity in line with regulations.

Special police forces hauled cement barriers and erected reinforcements around government buildings and banks. Armored personnel carriers deployed in many areas of the city.

The beefed up security followed the departure from Beirut of Qatari and Turkish mediators after two days of talks that apparently failed to resolve the differences between Lebanon's main rival factions and bring them back together in a coalition government.

Hezbollah denies any role in Rafik Hariri's killing and forced the government's collapse last week when Saad Hariri refused to renounce the tribunal and to pull Lebanon's funding for the court. Eleven ministers from Hezbollah and its allies resigned from the Cabinet, enough to force the government to fall.

The militant group says the tribunal is a conspiracy by Israel and the United States.

There are concerns that Hezbollah supporters may take to the streets, setting the stage for sectarian fighting similar to Shiite-Sunni street clashes that killed 81 people in 2008.

Hariri was Lebanon's most prominent Sunni leader.

The collapse of Lebanon's Western-backed government was a blow to the United States and its Arab allies, including Saudi Arabia and Egypt. It also suggests the competition over influence in Lebanon is tipping in favor of Hezbollah and its patrons Iran and Syria.

On Thursday, Secretary of State Hillary Rodham Clinton said any mediation from the outside must lead to stability and "a commitment to bringing those who committed the murders of Prime Minister Hariri and 22 others to account."

"I think that over the next days you will see a lot of activity within Lebanon itself," Clinton said. "And we stand ready, as do others in the region and beyond, to be of assistance."


Associated Press writers Elizabeth A. Kennedy and Zeina Karam in Beirut and Matthew Lee in Washington contributed to this report.