MADRID  - Basque militant separatist group ETA, which waged a bloody campaign for independence from Spain for more than four decades, said on Friday it had surrendered all its arms and explosives. 

The BBC cited what it said was a letter from ETA declaring it had handed all its weapons to civilian go-betweens and was now a disarmed organisation. The move stops short of a full disbanding of a group documented as having killed more than 850 people before declaring a ceasefire in 2011.  

Arnaldo Otegi, leader of Basque pro-independence party EH Bildu and who has served jail time for his links with ETA, said this marked the end of the armed fight for a separate state in northern Spain and south-western France. 

"We are entering an irreversible situation, violence will not be used to obtain self-determination and independence... We are happily and calmly looking forward to tomorrow," Otegi said. 

Otegi called for an independence referendum like that held in Scotland in 2014. A survey last October by pollsters Euskobarometro showed 29 percent of Basques strongly favoured independence and 37 percent had no desire for it. 

The middlemen are due to hand over the weapons to authorities on Saturday in the French city of Bayonne in a process first flagged in March by Basque activists. 

Spain's ruling Popular Party (PP) said it would not yield on its long-held refusal to negotiate with ETA. 

"They must disarm, disband, apologise and help to clear up crimes that are still unresolved," Education Minister Inigo Mendez de Vigo said at the government's weekly news conference. 

"They will get nothing from a democratic state like Spain," added Mendez de Vigo, whose government has resisted lobbying to move ETA prisoners to facilities close to the Basque Country. 

A government source said Madrid did not believe the group would hand over all its weapons. It is not clear if the process will be accepted by either the Spanish or French governments. 

Friday's letter, published in full on the BBC website, gave no details on how the handover would be carried out. 

The group, formed in 1959 during the dictatorship of General Francisco Franco, has been severely weakened in recent years after authorities arrested hundreds of its members and seized several of its weapons stashes. 

In Bilbao, the industrial city at the heart of the Basque region, residents were cautiously optimistic about the handover. 

"In my opinion certain conditions and guarantees have to be granted," said Antonio, who declined to give his last name. "They should negotiate in some aspects that are yet not clear ... not only weapons."