Bangladesh police banned all protests in the capital from Sunday and locked main opposition leader Khaleda Zia in her office in Dhaka as tension rose before the first anniversary of an election her party boycotted.
Zia had threatened to hold mass rallies in Dhaka to mark "Democracy Killing Day" on Monday -- the first anniversary of the polls that her Bangladesh Nationalist Party (BNP) and its Islamist allies refused to join on the grounds they would be rigged by the ruling party.
"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 S.R. Shimul Biswas told AFP.
Police banned all protests, meetings and demonstrations in the capital from 5pm (1100 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.  
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.
Zia was forced to spend the night at the party office despite attempting to leave by car, the aide said.
Police detained several people who tried to break through the security cordon to meet Zia in her office, live TV footage showed.     
Police Inspector Firoz Kabir denied that Zia was being forcibly detained in her office.
"We've not detained her, only her security has been enhanced. She is not leaving her office," he told AFP.
Police also stormed the home of the BNP deputy leader Fakhrul Islam Alamgir, Somoy Television said, but it was unclear whether he was at home at the time.
Senior BNP leader and key party spokesman Rizvi Ahmed fell ill at party headquarters. When he emerged, he was taken to hospital under police escort.
Zia had been attempting to visit Ahmed.
Tension has been rising since January 1, when Zia demanded fresh polls under a neutral caretaker government and threatened to bring the country to a halt.  
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.
Zia was confined to her home in the build-up to last year's election but was released after the polls.
Zia and her allies had alleged Hasina would rig last year's vote with the help of a biased election commission and "partisan" civil and security agencies.
The United States has said the polls did not credibly reflect the will of the people  
Since the controversial election, Hasina has consolidated her power by arresting opposition officials, prosecuting hundreds of thousands for violence in the run-up, and launching the trials of Zia and her eldest son on graft charges.
Scores of BNP activists have disappeared, with rights groups blaming security agencies.