DHAKA - Dissidents in Bangladesh's largest political party have ousted former prime minister Khaleda Zia as leader while she is under arrest on corruption charges, officials said Tuesday.

The move comes amid a worsening split within the Bangladesh Nationalist Party (BNP) between Zia's loyalists and so-called reformers attempting to revitalise the party in line with the emergency government's anti-graft drive.

Former finance minister M. Saifur Rahman, seen as a dissident in the BNP, said he was made acting party chief in Zia's absence after a marathon party meeting late Monday.

"Our aim is to unite the nationalist forces in the country," Rahman told reporters, adding that under his leadership the party would now adopt reforms to make it more dynamic.

Hafizuddin Ahmed, another former minister and a key BNP rebel, was also made acting secretary general in place of Zia loyalist Khandaker Delwar Hossain -- who is sick.

But a close aide to Zia said the move was "illegal and went against the constitution" of the party.

"We will not accept the decisions. They have no right to replace Khaleda Zia. She is still the party chief," said A.S.M Hannan Shah. "It's a part of a big conspiracy... They want to destroy the party."

Zia was arrested in September on charges of graft linked to the awarding of a multi-million-dollar government contract.

She has also been trying to fight a growing party rebellion, and had fired her deputy in the BNP hierarchy, Abdul Mannan Bhuiyan, for "conspiracy to split the party."

That sacking was also annulled by the latest party meeting, party rebels said.

The BNP was Bangladesh's last governing party, but has been in turmoil since elections were cancelled in January over opposition allegations of poll rigging.

Since then the country has been ruled by an army-backed emergency government, which has embarked on a campaign to clean up the country's notoriously dysfunctional and dynastic political landscape.

Zia, 63, has been one of the main targets, along with her arch-rival Sheikh Hasina Wajed, another former prime minister and the leader of the Awami League. She is also behind bars facing corruption charges.

The emergency government has promised to restore democracy by the end of 2008.

Leading political commentator Ataus Samad said the ouster of Zia did not appear to be the end of the drama.

"It was played out by a few behind closed doors. The so-called decisions obviously lacked credibility. It is very clear that a large section of BNP has not been consulted," said Samad.