With former prime minister Khaleda Zia in detention over graft charges, her Bangladesh Nationalist Party has made a dramatic change in the top leadership by appointing former finance minister Saifur Rahman as the party's acting chairman.

The highest policy making standing committee of BNP, in a midnight decision, also made former water resource minister and dissident leader Hafizuddin Ahmed as the new secretary general, but decided that Zia would remain as the party's chairperson.

Eight of the 12 members joined in a hurriedly called meeting, which also "disapproved" of Zia's "unilateral" order expelling party's secretary general and rebel leader Abdul Mannan Bhuiyan and two other leaders after her arrest on September 3 on corruption charges.

"The decisions were taken to maintain party unity," Rahman told reporters after the five-hour meeting at his house.

He said the BNP top brass agreed that they have faith in Zia, and her decision will be unanimously accepted once she was released.

Rahman said Zia-appointed Khondokar Delwar Hossain was removed as the secretary general due to his "poor health".

The overnight change visibly gave an upper hand to BNP's dissidents led by Bhuiyan as they were spearheading a campaign to "democratise" the party by clipping the chairperson's "absolute authority" in decision making process.

Hossain, also a standing committee member, did not join the meeting and could not be reached by the media for comments.

Bangladesh's military-backed interim government has launched a massive anti-graft campaign since a state of emergency was imposed in January with nearly 200 high-profile personalities, including Zia and her archrival Sheikh Hasina of Awami League, being jailed.

Zia, 62, won a reprieve in her battle to clear her name last week after the country's powerful Anti-Corruption Commission said it had found no evidence to prove at least two allegations against her.

Zia was investigated by the commission for alleged wrongdoing in connection with compensation for fires at a gas field operated by a US firm in 1997 and also for illegally awarding a mining concession.

Zia and her younger son Arafat Rahman Koko were arrested in September after the commission accused them of illegally influencing the selection of an operator for two state-run container depots in 2003.

Khaleda's influential elder son Tareque Rahman has been in jail since March on corruption charges.

Rahman said Zia's decision to expel Bhuiyan and joint secretary general Ashraf Hossain was "not approved" by the meeting.

But a close associate of Zia, asking not to be named, told the New Age that those who went to the meeting had "betrayed the party".

Two of the four members of BNP's standing committee are now in jail.