Veteran Marxist leader Harkishan Singh Surjeet, who was admitted to a hospital with an acute respiratory problem, has slipped into coma.

His condition remains critical.

"He is in coma and is not responding," said Dr Purushottam Lal, who is monitoring his condition at the Metro Hospital in Noida.

92-year-old Surjeet was admitted to the hospital on May 6.

"Though his vital organs are stable, his condition is neither better nor worse. He had seizures and was medicated for it and his brain is still functioning," he said.

Due to his failing health, Surjeet was, for the first time, not included in the CPI(M) Politburo at the party's 19th congress in April this year. He was instead designated as Special Invitee to the Central Committee.