Greek authorities say a far-left extremist convicted of 11 murders has been placed in intensive care after a 15-day hunger strike that has triggered violent protests by political sympathizers.

The health ministry says the condition of Dimitris Koufodinas, the main hit man of the November 17 terrorist group, is not life-threatening.

He was moved to intensive care for monitoring Friday in a hospital in the central town of Volos.

Koufodinas, 61, has vowed to continue his hunger strike "to the end" unless authorities allow him a new temporary prison leave. He had been granted six furloughs since late 2017, but last week judges ruled that he still poses a threat to society.

November 17 killed 23 people from 1975-2000. Koufodinas was convicted in 2003 and is serving 11 life terms.