Bangladesh police have banned all protests in the capital Dhaka from Sunday and locked main opposition leader Khaleda Zia in her office, ahead of the first anniversary of an election her party boycotted.

Zia had threatened to hold mass rallies in the capital to mark "Democracy Killing Day" on Monday marking a year since the polls that her Bangladesh Nationalist Party (BNP) and its Islamist allies refused to join, alleging the ruling party would rig the vote.

"She has been confined in her office. Police have cordoned off the area and barricaded [the] road. She wanted to see a sick party colleague around midnight, but they did not let her out," Zia's aide SR Shimul Biswas told the AFP news agency.

Al Jazeera's Tanvir Chowdhury, reporting from Dhaka, said Zia has been confined to her Gulshan office since Saturday night with police, including women officers, deployed outside her office.

Police banned all protests, meetings and demonstrations in the capital from 5pm (11:00 GMT) Sunday until further notice to prevent violence after the ruling party announced rival rallies.

"We imposed the ban as rival rallies by the political parties raised fears of clashes," Dhaka police spokesman Masudur Rahman told AFP.

Buses and ferries heading to the capital were halted, virtually cutting the city from the rest of the country, operators said, amid fears tens of thousands of opposition activists would march to Dhaka.

'Breakdown in democracy' 

The main opposition headquarters in central Dhaka was padlocked by police at midnight on Saturday, according to local television channels, with police vans barricading nearby roads.

A bus was torched near the office but there were no reports of injuries.  

Toby Cadman, an international human rights lawyer who has advised Bangladeshi opposition politicians on war crimes, told Al Jazeera that there has a "breakdown in democracy" in Bangladesh.

He said the country was "far from [being] a democracy" and that the authorities had tried to "shut down any form of protests; any form of criticism".

"There has been a general trend of curtailment of rights," Cadman said, adding that courts were being used to get rid political opponents.  

Zia was forced to spend the night at the party office, the aide said, despite attempting to leave by car.

Police inspector Firoz Kabir denied that Zia was forcibly kept in the office.

"We've not detained her, only her security has been enhanced. She is not leaving her office," he told AFP.

Opposition figures arrested

Police also stormed the home of the party's deputy leader, the private Somoy Television channel said, and arrested senior leader and key party spokesman Rizvi Ahmed, who fell ill and was taken to a hospital by police escort.

Zia had been attempting to visit Ahmed.

Tension has been rising in the politically volatile South Asian nation since January 1 when Zia demanded fresh polls under a neutral caretaker government and threatened to bring the country to a halt if her demand is not met.

BNP officials said at least 400 party supporters were arrested, including two other senior party figures, ahead of the poll anniversary.

Zia's decision to boycott the "farcical" election handed a walkover victory to her bitter rival Prime Minister Sheikh Hasina after no vote was cast in the majority of the parliamentary seats.

Zia was confined to her home in the build-up to last year's election, but was released after the polls.

Source: Al Jazeera and agencies