Violence has escalated in Nigeria on the third day of a strike to protest a massive fuel-price increase. Dozens of people have been injured in clashes involving civilians and security forces. Union leaders have complained of excessive force used on protesters.

Police fired bullets in several parts of Nigeria's main city, Lagos, to disperse demonstrators trying to prevent access to markets and to the main port.

In the capital, Abuja, there were clashes between union activists and market workers who refused to join the protest action. Security forces were deployed to defuse the situation, but instead triggered a stampede when they fired live rounds and tear gas into the air.

There have been reports of violence in Abuja and Lagos since Monday, but the strike appears now to be marked more by the rowdy demonstrations than by workers actually staying home.

The protest action Wednesday also spread to parts of Nigeria's oil-producing southeastern regions, where demonstrators lit bonfires on major streets.

The secretary general of the Nigerian Labor Congress, John Odah, said Tuesday union leaders were trying to convince police to use less force against protesters. "We have reports coming in to indicate that police are becoming very violent," said Mr. Odah, "and we are getting in touch with the hierarchy of the police establishment."

Union leaders have also failed to convince government officials to reverse the fuel price hike, despite several rounds of negotiations since Monday.

Retail fuel prices went up more than 50 percent last month after the government slashed subsidies to Nigerians. Union officials say staging the strike is the only way to begin a dialogue.

In a speech broadcast on television Tuesday, President Olusegun Obasanjo clearly enunciated the government position. He said it was time for Nigeria to make its oil sector more competitive, and that one way to do this is by ending the oil subsidies.

"Nigeria has lagged behind since 1960 because we do not have the courage to move as we should move and putting behind us the easy way out," said President Obasanjo. "Not fighting the issue of fuel subsidies is the easy way out, and nobody succeeds by following the easy way out. We must struggle. We must make sacrifices."

The government says the price rise is also needed to end internal shortages and to curb smuggling of cheaper Nigerian oil to neighboring countries.

Union leaders say ordinary Nigerians should not bear the brunt of reform. They say officials should crack down on corruption and fuel smuggling more effectively.

The main oil workers union is now threatening a shutdown of Nigeria's oil industry if the strike is not resolved by Sunday night.