WASHINGTON (AFP) - The United States blacklisted two Greek extremists Tuesday amid a row over Greece's new law which could see a bombmaker from a radical group accused of killing Americans released early from prison.

US Secretary of State John Kerry had personally voiced concerns to the new Greek government that under the legislation, Savvas Xiros, a bombmaker for the violent far-left November 17 group would be freed to serve the rest of his term under house arrest.

The shadowy movement was behind the 1975 killing of the CIA's Athens station chief, Richard Welch, and claimed responsibility for assassinating 23 people in scores of attacks on US, British, Turkish and Greek targets between the 1970s and 1990s.

But the Greek parliament brushed aside the US pleas and adopted the law late Monday, with the support of the leftist ruling party Syriza.

The State Department early Tuesday hit back, slapping terrorist designations on convicted November 17 hitman, Christodoulos Xiros, and Nikolaos Maziotis, the leader of the Revolutionary Struggle blamed for a 2007 rocket-propelled grenade attack on the US embassy in Athens.

It is believed Christodolous Xiros and Stavvas Xiros may be brothers.

Before its breakup in 2002, November 17 was one of Greece's most violent far-left organizations.

Christodolous Xiros was re-arrested in January after he vanished in 2014 while on furlough to visit his family in northern Greece, leaving the prison where he was serving multiple life sentences for a series of deadly attacks.

Maziotis had also escaped during his 2010 trial, but was re-arrested in July after a shootout in Athens' main tourist area in which four people were wounded, the State Department said.

The new terror designations mean that any of the two men's assets in the US will be frozen and Americans are banned from providing them with material support.

The bill adopted by the Greek parliament late Monday allows disabled prisoners who have served most of their sentences to see out the rest of their terms under house arrest. It also abolished controversial C-type jails, where some of the country's most notorious criminals are held.

Savvas Xiros, who is serving a life sentence, was arrested in 2002 after suffering serious eye injuries in a failed bomb attack. He is also said to be suffering from multiple sclerosis.