KUALA LUMPUR - MALAYSIA'S prime minister has convoked the ruling party's top policy-making body in emergency session, seeking to impose his authority after the dramatic defection of former premier Mahathir Mohamad.

Datuk Seri Abdullah Ahmad Badawi was due to chair a special supreme council meeting of the United Malays National Organisation (Umno) at 1200 GMT (8pm Singapore time) on Wednesday, his office said.

Umno has been in turmoil since its poor showing in March elections, which created political uncertainty and spooked investors in the South-east Asian country.

Tun Dr Mahathir's bombshell resignation on Monday from the party he led for 22 years came with a call for other Umno members to quit with him. A meeting of lawmakers on Tuesday ignored the call and rallied behind Datuk Seri Abdullah.

Tun Dr Mahathir said he was resigning in a bid to force Datuk Seri Abdullah out, but the prime minister said he would not resign.

Analysts said the most likely outcome of the Wednesday night meeting was a reaffirmation by Umno leaders of their support for the prime minister.

'At this point, there are so many factions and alliances within the leadership. But he will probably get the support of the majority within the Supreme Council,' said Mr Lee Hock Guan, senior fellow with Institute of South East Asian Studies in Singapore.

Tun Dr Mahathir's defection from Umno came three days after Datuk Seri Abdullah ordered the attorney-general to investigate the former premier and five others on possible offences over the appointment of judges while he was in power.

It added to concerns about the continued hold on power of the Barisan Nasional (BN) coalition, of which Umno is the dominant partner. An emboldened opposition, headed by Tun Dr Mahathir arch-foe Anwar Ibrahim, is seeking to wrest power by wooing BN defectors.

Datuk Seri Anwar, a former deputy premier, said Tun Dr Mahathir's resignation was indicative of Umno's worsening crisis.

'The internal problems of UMNO are clearly deteriorating beyond any hope of recovery,' he said, and called on Malaysians to join his group.

Umno, backbone of the 14-party BN that has ruled since independence from Britain in 1957, holds 79 of its 140 seats.

The opposition is a loose alliance of Islamists, a Chinese-based party and the multiracial PKR, and needs to gain just 30 seats to win a simple majority and form the government.