Osamu Maruoka, a former member of the Japanese Red Army, died at a prison hospital Sunday morning while serving a life sentence for a series of hijackings, sources close to him said.

While the cause of death was not immediately known, Maruoka, 60, had unsuccessfully sought to have his sentence suspended last year on the grounds that he suffers from a serious heart condition.

Maruoka conspired with Palestinian guerrillas in hijacking a Japan Airlines plane over Amsterdam in 1973. Together with four accomplices he also hijacked a JAL jumbo jet over India in 1977 and forced it to land at Dhaka airport in Bangladesh.

He was arrested in Tokyo in 1987 after entering on a forged passport, put on trial and given a life sentence, which was finalized by the Supreme Court in 2000.