COLOMBO, Sri Lanka--A car bomb exploded yesterday at the crowded main bus terminal in the heart of the Sri Lankan capital, and officials said as many as 150 people were killed and more than 200 were injured.

The explosion occurred at about 4:45 p.m. (7:15 a.m. EDT), a time when many workers were leaving their offices in this city of 750,000 people.

The blast was the first in Colombo since a series of fatal bombings last May that were blamed on Tamil guerrillas. Attacks by Tamil insurgents killed at least 142 people in eastern Sri Lanka in the past week.

The government issued a statement blaming the bombing on two Tamil separatist groups, the Liberation Tigers of Tamil Eelam and the Eelam Revolutionary Organization of Students.

Shortly after the explosion, mobs of Sinhalese civilians stoned Tamil-owned shops about a half-mile from the bus terminal. Police dispersed the crowd.

There was no immediate claim of responsibility for yesterday's blast.

Rescue work was hampered by heavy rainfall, and police comandeered cars, buses and trucks to help take the injured to hospitals.

The army cordoned off the area around the bus terminal, and police imposed a curfew on the Colombo district.

The United News of India said some witnesses at the scene said the bomb apparently was in a car parked in front of a branch of the Bank of Ceylon near the bus terminal. Police said they could not immediately confirm the report.

The Tamils, who are a minority in this island nation, have been fighting for four years for a separate homeland.

Beginning just before midnight Sunday, Tamil guerrillas burst into four houses in the remote Sinhalese village of Vannela, tied up 15 villagers and shot them to death.

On Friday, Tamil guerrillas killed 127 civilians, mostly Sinhalese, after dragging them from buses and other vehicles on a jungle road 10 miles outside Vannela.

Tamils, most of whom are Hindus, account for 18 percent of the 16 million people on Sri Lanka, an island off the southern coast of India. They claim they are discriminated against by the majority Sinhalese, who are Buddhists.

The Tamil rebels are battling to establish an independent homeland in the island's northern and eastern provinces, where most of the Tamils live. President Junius R. Jayewardene's government has proposed provincial councils to give greater autonomy to the north and east, but refuses to consider an independent Tamil nation.