DHAKA — Four opposition activists were killed and nearly 200 people injured on Sunday when police opened fire at large Bangladesh Nationalist Party (BNP) rallies in the southeast.

The shootings happened in the towns of Chandpur and Laksmipur after the party held demonstrations to demand that the government resign in a dispute over electoral reforms, police said.

"They attacked policemen with stones and bricks. We fired back in self-defence. Two BNP activists were killed," Chandpur police deputy chief Amir Zafar told AFP.

Zakir Ahmed, head of Chandpur police station, said the clashes erupted after about 7,000 BNP activists tried to gather at a school ground without first obtaining permission from the authorities.

"We first shot tear gas to disperse them. But they became more violent," he said, adding 100 people -- including 30 policemen -- were injured.

In Laksmipur, one person died when police fired rubber bullets and tear gas at more than 4,000 activists after they "became unruly and attacked police with guns", local police chief Golam Sarwar said.

"Two persons were injured seriously during the clashes. One died on the way to hospital and another was rushed to a clinic in Dhaka in critical condition," he said, adding 30 others sustained minor injuries.

Sub-inspector Yasmin Ara told AFP the critically injured person, also a BNP activist, died on the way to hospital.

Police also fired rubber bullets and tear gas at thousands of opposition supporters in three other district towns in the country's west, south and north, leaving more than 50 people hurt.

Authorities earlier banned rallies planned on Sunday in the capital Dhaka over fears of violent clashes between the BNP and the ruling Awami League party.

The BNP and its Islamist allies had called for a mass demonstration to demand the government stand down.

But the Awami League also said it would hold a rally in central Dhaka on Sunday, sparking the police decision to outlaw any political rallies that day.

The two parties have now shifted their programmes to Monday.

Bangladesh has a history of violent clashes between political activists, and the BNP has recently enforced a series of strikes in a new wave of unrest.

The South Asian nation of 150 million people witnessed deadly political violence in October 2006 when two major parties announced rallies on the same day, leading to the deaths of at least a half dozen activists.

Opposition anger was fuelled when the government led by Prime Minister Sheikh Hasina last year scrapped a system for overseeing elections.

The next national election is due to be held by early 2014.