"He is not well. A CT scan has been done and doctors are holding consultations," former West Bengal chief minister Jyoti Basu told reporters after a meeting of top leaders at the party's Alimuddin Street office in central Kolkata Sunday.

Central leader Sitaram Yechuri also reportedly attended the meeting.

A blood clot in Biswas' brain was removed during the surgery, CPI-M Politburo member and Left Front chairman Biman Bose said, adding that there is no further deterioration in his condition. However, he continued to be critical.

Doctors at Woodlands Nursing Home, where he was admitted Saturday night after the cerebral attack around 9 pm, said he was under observation and nothing could be said before Monday.

Another CPI-M leader said a six-member medical board has been constituted for Biswas, the man credited with the gradual liberalisation of the party from its hardline approach in West Bengal.

The sudden health problem of Anil Biswas, 62, came as a big jolt to the party in the run-up to the assembly elections next month.

Some poll meetings of Chief Minister Buddhadeb Bhattacharya, whose policies are backed by Biswas, have been cancelled.

A member of the party's Politburo since 1998, Biswas became the state secretary of the CPI-M the same year.

A former editor of the party mouthpiece in Bengali "Ganashakti", 62-year-old Biswas is s the brain behind the party's important decisions in West Bengal politics.