Former Bangladesh prime minister Sheikh Hasina was arrested from her home in the capital on Monday and remanded to police custody for a month, her party said.
It was not immediately clear on what charges Hasina was detained, but she was previously accused of extortion and corruption during her term in office from 1996 to 2001.
Timeline of Bangladesh crisis
Oct 2006: Violent protests over govt's choice of a caretaker administration to take over when Premier Zia completes her term at the end of the month. President Ahmed steps in and assumes caretaker role for period leading to elections due in Jan 2007.
Nov 2006: A 14-party opposition alliance led by the Awami League campaigns for controversial election officials to be removed. Chief election commissioner MA Aziz steps aside.
Dec 2006: Election date set at Jan 22. Awami alliance says it will boycott the polls. Awami leader Sheikh Hasina accuses President Ahmed of favouring her rival.
Jan 2007: A state of emergency is declared amid violence in the election run-up. President Ahmed postpones the Jan 22 poll. Fakhruddin Ahmed takes over as head of caretaker Admn.
Mar 2007: Six Islamist militants convicted of countrywide bomb attacks in 2005 are hanged. They include the leaders of Jagrata Muslim Janata Bangladesh and Jamaat-ul-Mujahideen.
Apr 2007: Sheikh Hasina is charged with murder. Begum Khaleda Zia is under virtual house arrest. Several other politicians are held in an anti-corruption drive.
May 2007: Interim government eases restrictions on former prime ministers Sheikh Hasina and Begum Khaleda Zia.
"The court has ordered Hasina detained for one month," Begum Motia Chowdhury, a senior leader of her Awami League party, told reporters outside the Dhaka metropolitan court where she was brought amid tight security.
Hasina has denied the charges previously. "We will come out soon with all the details," her lawyer told reporters.
Bangladesh is under a state of emergency imposed by the country's army-backed interim administration which took charge in January and launched a crackdown on politicians ahead of elections planned for late next year.
More than 170 political figures including Tareque Rahman, the son of Hasina's rival and former prime minister Begum Khaleda Zia, have been detained for graft and abuse of power.
Hundreds of police and elite Rapid Action Battalion force surrounded Hasina's home since Sunday midnight. They entered the house early on Monday, put her on a security vehicle and drove to the court, witnesses and her party officials said.
Hasina's son said his mother's detention was a conspiracy to remove her from politics.
"I have spoken to my mother. She told me about the police action ... it's part of a deep-rooted conspiracy," Sajeeb Wazed Joy told reporters in Dhaka by telephone from the United States, where he lives.
"I have no plan to return to Bangladesh immediately but will try to organise a protest worldwide," he added.
"The law enforcing agencies are going beyond their limits."
Students staged small protests at Dhaka University but were driven back by police, witnesses said.
Hasina and Khaleda have alternated as Bangladesh's prime ministers for the past 15 years, and were top contenders for power in the next election.
Khaleda also faces charges of extortion and abuse of power.