Eta claimed various bomb attacks this summer

Three masked and armed militants made the announcement in a video received by a Basque pro-independence newspaper.

They said they were fighting for the Basques' right to decide their own political future.

The group has largely kept a low profile since the Madrid train bombings by Islamist militants in March.

In the video sent to Basque newspaper Gara, the group's representatives said there was a "new opportunity" to end the conflict but did not make clear why.

They warned that Eta would "respond with arms at the ready to those who deny us through the force of arms".

'Weakened'

The BBC's Katya Adler reports from Madrid that the statement is Eta's most detailed public comment since the 11 March train bombings in Madrid in which 191 people died.

The Spanish authorities initially blamed the group for those attacks, later saying they had been organised by Islamic extremists.

Eta has claimed, or been blamed for, more than 800 deaths since launching a campaign in the late 1960s for an independent Basque homeland straddling northern Spain and south-west France.

But the group is thought to have been weakened following a series of high-profile arrests.

These were largely due to improved co-operation between the Spanish and French police forces following the 11 September 2001 attacks on New York and Washington.

Power targeted

No-one has been killed in an Eta attack since May of last year but its video broadcasts the message that the group is still around and prepared to fight, our correspondent says.

At the weekend, Eta claimed responsibility for a series of bombs which reduced power transmission between France and Spain.

It also said it launched a string of minor attacks this summer in resorts across Spain's northern coast.