Officials say a far-left Greek extremist serving 11 life terms for a string of assassinations is in the hospital following a five-day hunger strike over prison authorities' refusal to grant him temporary leave.

Dimitris Koufodinas, 61, was being treated in the central town of Volos Tuesday, health officials said.

Koufodinas was the main hit man for the November 17 group, which killed 23 people, including Western diplomats, between 1975-2000. N17 was eradicated in 2002.

Since late 2017 Koufodinas has been granted six furloughs — once after a hunger strike — and transferred from a maximum-security Athens prison to a laxer penitentiary near Volos.

That has sparked protests from relatives of his victims and U.S. officials.

Anarchist groups in Athens plan a march in support of Koufodinas later Tuesday.