Police and protesters clash in Dhaka

Just before sunrise in Dhaka, protesters from the opposition Bangladesh National Party (BNP) set fire to and smashed up a police vehicle.

After daybreak, a large number of activists took part in a sit-down protest in the capital.

Violence broke out at dusk, however, when police used rubber bullets and tear gas to disperse a crowd of stone-throwing protesters in Dhaka's southern Jatrabari district.

At least 25 people were said to have been injured in the clashes.

A coalition of 18 opposition parties had earlier called for roads to be blocked across the country to highlight calls for the restoration of a constitutional provision allowing a non-partisan caretaker administration to oversee the polls due in 2014.

Prime Minister Sheikh Hasina's government scrapped the 15-year-old provision last year after the supreme court ruled it unconstitutional, saying the constitution allows only popularly elected people to run the government.

The opposition, led by former Prime Minister Khaleda Zia, says the change will allow Hasina to rig the election.

Hasina denies the allegation.

During the sit-down protest, Joynal Abedin Faruq, a BNP politician, said that if the government creates "obstacles to our movement to ensure our democratic rights, more protests will be held in the coming days."