Deadly clashes have erupted on the streets of Bangladesh on the first anniversary of elections as police besiege the main opposition leader in her office.

Police say two supporters of the opposition Bangladesh Nationalist party have been killed in clashes with ruling party activists in the northern town of Natore, fuelling tensions on a day that the BNP has declared “democracy killing day”.

The BNP leader, Khaleda Zia, despite being confined to her Dhaka office, has urged activists to take to the streets in their thousands as part of a campaign to force the prime minister, Sheikh Hasina, to hold fresh multi-party polls.

A local police inspector said the two BNP activists were shot dead during clashes with supporters of Hasina’s Awami League. At least 15 people were injured, Mohammad Fariduddin added.

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

Zia issued the call for mass protests from inside her office, where she has been confined since Saturday night after police cordoned off the area.

Authorities stepped up their siege on Monday by parking 11 trucks outside her office in a blockade designed to thwart any attempt by her to lead the protests in person.

The trucks, laden with sand and bricks, were wedged outside the gates of Zia’s office in the upmarket Gulshan district and at the beginning of the road leading to the building.

Riot police, flanked by armoured vehicles equipped with water cannon, prevented anyone from entering or leaving the premises.

“The trucks have been parked in an effort to step up her security,” the Gulshan police chief, Rafiqul Islam, told AFP.

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

Hasina, who has been in power since 2009, was re-elected on 5 January 2014 in what was effectively a one-horse race after the BNP and about 20 other opposition parties boycotted the polls over rigging fears.

Zia’s boycott was sparked by her archrival’s refusal to step down before the election and allow the contest 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 a majority of members in the 300-seat parliament were returned unopposed, handing Hasina another five years in power.

Voting was overshadowed by firebomb attacks on polling booths and clashes that left about 25 people dead.

Many of the BNP’s leaders have since been detained or charged in connection with the election violence, hampering their efforts to press for new polls.

BNP headquarters in central Dhaka was padlocked by police at midnight on Saturday, with police vans barricading nearby roads.

BNP officials said at least 500 supporters have been arrested, including two senior party figures, ahead of the poll anniversary. Scuffles broke out near Zia’s office Sunday when a former president, Badruddoza Chowdhury, was turned away from meeting her. “It’s an insult to democracy,” he said.

Zia’s lawyer, Khandakar Mahbub Hossain, did manage to meet Zia on Sunday, telling reporters afterwards that she had asked people to “continue protests until the government is toppled”.

Some bus and ferry services heading to the capital were also suspended at the weekend in a move likely to reduce the number of protesters trying to reach Dhaka.

Hasina, who has consistently rejected calls for fresh elections, was to deliver a televised address to the nation on Monday night.

The violence on election day last year was the culmination of the bloodiest year of political unrest in Bangladesh’s short history, with tensions also heightened by the death sentences passed on leading Islamists over their role in the 1971 independence war.