Baton-wielding riot police fired tear gas and rounded up dozens of demonstrators in Bangladesh on Tuesday during a general strike called to protest a weekend grenade attack that killed 20 people and wounded hundreds at an opposition political rally.

The violence broke out after police tried to block hundreds of protesters from taking to the streets, witnesses said. Demonstrators waved clenched fists and shouted, "Down with the government!"

At least 25 people were injured in the clashes in the capital, Dhaka, and police took about 50 protesters into custody, the witnesses said. Streets in the city of 10 million were empty of most vehicles except rickshaws.

Similar clashes, injuring about 100 people, erupted on the eve of the dawn-to-dusk strike, called by the main opposition Awami League party and backed by several leftist parties, the United News of Bangladesh news agency reported.

The protest shut down shops and schools and disrupted traffic across the country.

Opposition activists threw stones and bricks at public buses in downtown Dhaka, injuring at least three passengers, the news agency said. Train services on several routes were halted as strike supporters barricaded tracks or attacked station employees.

No one has claimed responsibility for the grenade attack, which took place Saturday while opposition leader Sheikh Hasina was speaking outside her Awami League headquarters . But Hasina, who was unharmed, has blamed Prime Minister Khaleda Zia's administration. The government has denied involvement.

Fearing renewed violence during the two-day strike that began Tuesday, officials deployed more than 5,000 police and paramilitary troops in the capital.

Riot police in Dhaka detain an activist of the opposition Awami League party.