Lebanese mourned their slain ex-premier Tuesday with noisy street processions, while the country's interior minister suggested a homicide bomber aided by "international parties" may have been behind the assassination of Rafik Hariri (search).

Lebanon's government, still in shock from the bombing that left Hariri and 16 others dead, came under mounting pressure to bring the assassins to justice. Many in Lebanon blamed the attack on Syria.

International leaders are expected to join tens of thousands at Hariri's funeral on Wednesday as the outpouring of grief and anger following the billionaire tycoon's death continued.

Dozens of angry Hariri supporters attacked Syrian workers in the former leader's hometown of Sidon, in southern Lebanon, lightly injuring five and shattering the windows of a Syrian-owned bakery. Syria has denied involvement and condemned the attack, but many Lebanese have increased demands on Damascus (search) to withdraw its 15,000 soldiers from the country.

Syria deployed its forces to Lebanon during the 1975-90 civil war to stop the country from falling apart and remained after the conflict ended. Its continued presence is a source of frustration for many Lebanese and for the international community, particularly Washington.

Interior Minister Suleiman Franjieh suggested a homicide bomber may have targeted Hariri's heavily protected motorcade as its cruised through Beirut's Ein-Mreisseh neighborhood. He said the location of the crater in the middle of the road indicated the bomb-laden car was approaching the motorcade, attempting to ram it or to bypass it.

"For sure, someone was driving the car. He could be a homicide bomber who blew himself up," the minister said, hinting of a network behind the assassination.

Franjieh, however, said he could not confirm the homicide attack theory and was awaiting DNA results from those killed.

While most suspicion has fallen on Syria (search) or its supporters here, possibilities include rogue Syrian intelligence operatives, or even factions among Lebanon's myriad religious groups. Responsibility claims by previously unknown Islamic militants were not considered credible, with Justice Minister Adnan Addoum warning they could be an attempt "to mislead the investigation."

At the bomb scene, explosives experts combed rooftops and the street, searching for evidence as residents cleared debris from their balconies.

Thousands of mourners marched through Beirut's streets in separate processions to pay tribute to Hariri and condemn his killers. "Syrians Out!" chanted several hundred protesters wearing business suits, while motorcades of supporters elsewhere honked car horns while driving through the capital in cars pasted with Hariri's pictures.

The United States recalled its ambassador, expressing "profound outrage" over Hariri's assassination, said State Department spokesman Richard Boucher. He did not accuse Syria of being involved in the bombing.

U.N. Secretary-General Kofi Annan (search) called for an investigation, while the Security Council called on the Lebanese government "to bring to justice the perpetrators, organizers and sponsors of this heinous terrorist act."

The Syrian ambassador, Imad Moustapha, on Tuesday accused people of trying to use the tragedy for political advantage. He also suggested damaging Syria was part of a plot.

"Syria has nothing to benefit from what has happened," Moustapha told CNN. "Certain factions are trying to damage Syria because of what has happened, and this indicates a sinister plot that does not only stop at the murderous act of assassinating Rafik Hariri but also trying to point fingers at Syria."

Hariri, whose wealth was estimated at $4 billion and who served as Lebanon's prime minister for 10 of 14 years following the war, was credited with rebuilding the ravaged country. He was also believed to oppose Syria's control of his country and resigned after a Damascus-backed constitutional amendment extended the presidency of Emile Lahoud, a close Syrian ally and a Hariri rival.

The killing came ahead of national elections expected in April and May, in which Hariri planned to run. While not publicly rebuking Syria, Hariri was seen as quietly opposing Damascus' role in Lebanon, and his death leaves a void at a time when some Lebanese are seeking greater independence.

The bombing also intensified tensions between the United States and Syria, which is accused by Washington of supporting anti-Israeli militants and insurgents attacking U.S.-led coalition forces in Iraq. Syria has denied the charges.