BEIRUT (AP) -- Tens of thousands packed into a city square Wednesday to mark the second anniversary of former Prime Minister Rafik Hariri's assassination as hundreds of troops were deployed a day after bus bombings killed three people.

Troops in full combat gear and armored cars deployed in and around Martyrs' Square, where the country's two main rival groups were present: government supporters commemorating Hariri's death and opposition supporters continuing their daily sit-in to demand the government's resignation.

The soldiers set up a razor wire barrier to separate the two groups, and police conducted body searches of people arriving in the square.

At exactly 12:55 p.m. -- the time of the explosion that killed Hariri and 22 others -- the crowd fell silent except for a muezzin making the Islamic call to prayer and the tolling of a church bell. Standing at the speaker's podium, Hariri's son, Saad, and sister, Bahiya, prayed.

The speakers addressed the crowd from behind bulletproof glass, calling for approval of a UN-created tribunal to try suspects in the Hariri assassination. The tribunal's ratification has been held up by political dispute.

A respected Shiite cleric from southern Lebanon, Ali Amin, criticized the Shiite-backed opposition parties, Hezbollah and Amal, for failing to strike a deal with the government. The two parties withdrew from the Cabinet last year.

"Our fate is through agreement and the mechanism is to return to the logic of the state and institutions," said Amin, without naming Hezbollah and Amal. Referring to the failure to ratify the tribunal, he said "it was strange" to oppose justice.

Explosions stoke fears

Tuesday's explosions on commuter buses on a busy mountain highway northeast of Beirut stoked fears of turmoil as the country prepared to mark the 2005 assassination of Hariri, the nation's most prominent politician and the leader credited with rebuilding the country from the destruction of the 1975-90 civil war.

Lebanon has suffered a series of bombings during the past two years, mostly targeting anti-Syrian figures, but Tuesday's attacks were the first that seemed intended to cause maximum casualties among civilians of no political affiliation.

"We will hunt down the criminals and confront them," Prime Minister Fuad Saniora vowed in a televised speech Tuesday evening.

The UN Security Council condemned the bombing, urging all Lebanese parties to exercise restraint and stressing its support for the government.

The pro-government majority in parliament said it held "the Syrian regime fully responsible for this despicable crime." Syria routinely denies involvement in Lebanese unrest.

Government supporters said the blasts were intended to scare people away from Wednesday's commemoration. They urged their supporters to show up in large numbers.

The government, which has faced down months of demonstrations calling for its resignation, declared Wednesday a national holiday, closing schools, universities, banks and public institutions in a move that would allow for a big turnout.

In a bid to allow the anniversary to pass peacefully, the major opposition figure, Hezbollah leader Hassan Nasrallah, praised the late Hariri in a letter published on the front page of As-Safir newspaper Wednesday. Nasrallah said Hariri's killing in a massive truck bomb on Feb. 14, 2005, was a loss for the whole country.

National demand

Finding the perpetrators has become "a collective national demand," Nasrallah wrote.

Hariri and 22 others were killed in a huge explosion that occurred as his motorcade was passing through central Beirut. He was buried a few blocks away from the site. Outrage over the assassination forced Syria to withdraw its troops from Lebanon two months later, ending a 29-year presence.

A UN investigation into the assassination is continuing, but Lebanon has been hit by a string of bombings in the past two years that many government supporters blame on Syria. Syria has denied any role in the attacks, including the Hariri assassination.

None of the perpetrators has been caught from the series of bombings, which killed four anti-Syrian figures, wounded two others, and occasionally have struck public areas, killing three people.

Tuesday's bus bombings, however, were the first time that an attack appeared aimed to exact maximum casualties on civilians with no political affiliation.