Clashes between supporters of Bangladesh's opposition and ruling party have erupted in several cities as  security forces continued their siege of opposition leader Khaleda Zia's office, preventing her from leaving.

Monday marks the first anniversary of last year's controversial poll, and Zia had urged her supporters to take to the streets in a bid to force the government to call a fresh election.

Police said two activists of the opposition Bangladesh Nationalist Party, led by Zia, were killed in clashes with supporters of the ruling Awami League in the northern town of Natore.

The victims were identified as men in their 20s and shot by assailants on motorbikes, fuelling tensions on a day which the BNP had declared to be "Democracy Killing Day".

Zia's BNP along with 20 other opposition parties boycotted last year's election, citing a biased election commission, among other reasons. About 500 people were reportedly killed in the run-up to the election.

Authorities stepped up their siege of Zia's office in Dhaka on Monday by parking 11 trucks outside in a blockade designed to thwart any attempt by her to head protests in person.

Al Jazeera's Tanvir Chowdhury, reporting from the capital, said Zia - confined to her office since Saturday - was trying to force her way out.

"Khaleda Zia is planning to come out of her office any time now, [but] the main gate is locked and [the] entire area is cordoned off and barricaded by trucks," he said.

Police said the office had been cordoned off "in an effort to step up her security".

Lawyers protesting 

Security forces have been deployed in various places across Dhaka and the street leading to Zia's home has been blocked.

Violence broke out in Dhaka and in around half a dozen towns as police and Awami League followers clashed with hundreds of BNP protesters, local television channels said.

Hundreds of pro-opposition lawyers joined the protests at the sprawling complex which houses the Supreme Court, where they waved black flags to signal the "death of democracy". Police locked the gates into the main building, confining the protesters to the grounds outside.

Zia’s spokesman said the BNP chief would attend a mass rally although getting out of her office would be difficult.

"She has urged people to join a mass rally today. She would also try to join the protest," spokesman Maruf Kamal Khan told reporters.

Zia's boycott last year was sparked by her arch rival's refusal to step down before the election and allow it to be organised by a neutral caretaker administration. The caretaker system was in place for previous polls.

The boycott by the BNP and its allies meant most members in the 300-seat parliament were returned unopposed, handing Prime Minister Sheikh Hasina another five years in power.

Source: Al Jazeera and agencies