The Greek authorities are claiming a major breakthrough, with the arrest of a man said to be a leader of the left-wing group November 17.

From various evidence we began to build a picture of the ideological instructor of the organisation

Police Chief Fotis Nassiakos

Until last month, police had failed to arrest a single suspect in their 27-year campaign against Europe's most elusive urban guerrilla organisation.

The alleged leader has been identified as 58-year-old Alexandros Giotopoulos, a French-born academic who was picked up on the Aegean island of Lipsi on Wednesday.

He was sharing his time between France and Greece and living under the assumed name Michalis Economou.

His fingerprints matched prints found in a November 17 hide-out earlier this month.

'Mastermind'

Moreover, police say Mr Giotopoulos fits the profile of the brain behind the group.

"From various evidence in the investigation we began to build a picture of the ideological instructor of the organisation and the writer of its proclamations," Police Chief Fotis Nassiakos said.

Police say Giotopoulos fits the leader's profile

The suspect is the son of Dimitris Giotopoulos, a well-known 1930s Communist and follower of Leon Trotsky.

Alexandros Giotopoulos is believed to have been active in the Paris-based student opposition to the military dictatorship which ruled Greece between 1967 and 1974.

After the fall of the junta, left-wing sentiment remained strong in Greece and defined a generation of socialist politicians.

November 17 rode a wave of anti-American sentiment that grew out of a deeply-held perception among many Greeks that the United States supported the junta.

American, British and Greek authorities have for years suspected the group's leaders may have had their ideological roots in the movements that fuelled France's student revolt in May 1968.

Family

The three other suspected members arrested so far, however, have no known history of political involvement.

Savvas Xiros was arrested last month

Savvas Xiros, who was picked up by police on 29 June, was a religious icon painter and the son of an orthodox priest.

The other two - Xiros's brother Vasilis and a close friend of theirs - also appear to have led ordinary, middle-class lives.

One of the group's key assets was that they were a close-knit family.

Police say the three have confessed to killings, bomb attacks, and robberies.

If found guilty they face sentences from 10 years to life in prison.