It's not clear whether the BNP will take part in the polls
A court in Bangladesh has ordered that three former ministers, including key allies of former PM Khaleda Zia, be remanded on corruption charges.
Among those who were sent to jail is the leader of the Jamaat-e-Islami, Motiur Rahman Nizami.
His party is a key partner in Ms Zia's Bangladesh Nationalist Party (BNP)-led alliance.
The three were charged by the Anti-Corruption Commission for illegally leasing out a coal mine in the north.
Another former minister was arrested on Sunday.
Correspondents say that the arrests throw further confusion over whether the BNP and its allies will take part in parliamentary elections scheduled for next month.
The former ministers are alleged to have made a deal with a foreign company - ignoring other lower bidders - to develop the coal mine.
Their lawyers insist that they are innocent and that the charges against them are "politically motivated". The next hearing of the case will take place on Thursday.
Thousands of Jamaat supporters protested near the court as the men were taken to jail.
The elections are due to be held on 18 December, with the four-party alliance led by the BNP already threatening to boycott the vote.
The country's army-backed caretaker government is keen to ensure the polls are credible and has released Khaleda Zia - the BNP's leader and former prime minister - from detention to secure her party's participation.
A report by the monitoring group Transparency International in June said that corruption in the country has continued to thrive since the interim government took power last year.
In some sectors of the country corruption had actually increased since January 2007, it said.