In a video obtained exclusively by the BBC, the group said it took the decision several months ago "to put in motion a democratic process". Three hooded Eta fighters are shown sitting behind a desk with the Eta flag pinned up behind them. The figure in the middle reads out a prepared statement defending Eta's campaign of violence, but towards the end she says the group now wants to achieve its aims by peaceful, democratic means.

The Basque interior minister called the statement "insufficient". Madrid has previously insisted that Eta renounce violence and disarm before any talks.

Eta's violent campaign has led to more than 820 deaths over the past 40 years. It has called two ceasefires in the past, but abandoned them both.

This latest announcement comes after the arrests of numerous Eta leaders and during an unprecedented period of debate within the Basque nationalist community over the future direction of policy.

Eta has been coming under increasing pressure to lay down its weapons.