BEIRUT, LEBANON - Lebanon's long-simmering political crisis erupted into gunfire and explosions Wednesday when a labor strike devolved into clashes between supporters of the government and those of Hezbollah.

Demonstrators supported by the militant Hezbollah protested the U.S.-backed government's economic policies and paralyzed much of Beirut with roadblocks of burning tires. The strike turned violent when both sides began throwing stones at each other, and gunfire and explosions rang out in some areas for brief periods.

The cause of the explosions was not immediately known. There were a few injuries reported, mostly from the stone throwing.

The clashes threatened to degenerate into an all-out sectarian conflict. Shiite Hezbollah seized the offices of a major Sunni group, and the fighting spread to several mixed Sunni-Shiite neighborhoods.

Most Sunnis back Prime Minister Fuad Saniora's government, while Shiites generally support the opposition led by Hezbollah, which the U.S. has labeled a terrorist organization.

The Sunnis' spiritual leader denounced the militant Shiite faction and appealed to the Islamic world to intervene.

"Sunni Muslims in Lebanon have had enough," Grand Mufti Mohammed Rashid Kabbani said in a televised address from his office, demanding an "end to these violations."

In unusually harsh words, he called Hezbollah "armed gangs of outlaws" and called on the group's leaders to withdraw from Beirut's Sunni neighborhoods.

Shiite opposition supporters remained on the streets after sunset, and many of the blocked roads remained closed, indicating the protest will likely continue at least until Hezbollah leader Hassan Nasrallah speaks at a planned news conference today.

Pay prompts protest

Wednesday's strike was called by labor unions after they rejected a government pay raise offer as insufficient. It was largely confined to Shiite areas that back the opposition.

Striking workers caused the delay or cancellation of dozens of arriving and departing flights at Beirut's airport. Flights resumed later, but the roads to the airport remained closed, trapping scores of arriving passengers in the terminal.

Hezbollah supporters seized two local offices of Sunni parliamentary majority leader Saad Hariri's group, security officials said.