Spanish Prime Minister Jose Luis Rodriguez Zapatero has thanked British leader Tony Blair for his guidance on the peace process in the Basque region.
Eta announced a permanent ceasefire in March
Mr Zapatero said Mr Blair had given him advice based on his experience in the peace process in Northern Ireland.
Mr Blair said ending conflict was a "difficult and complicated process".
Spain's government has been attacked by the opposition Popular Party (PP) for offering talks with Basque separatists Eta, who declared a ceasefire in March.
Correspondents say that Mr Zapatero's very public display of gratitude will be seen in Spain as a rebuke to the PP for withholding support from the talks.
Despite the announcement of a permanent ceasefire, Eta said last month that it would not give up its weapons until it was independent of Spain.
Mr Zapatero's government has said it will hold talks with Eta but has ruled out granting the Basques in north-western Spain full independence.
After talks in Madrid, Mr Zapatero said he wanted to thank Mr Blair "publicly for his government's support to our government in this difficult process".
"We have been talking about the peace process in the Basque country and I have heard a lot about the peace process in Northern Ireland," Mr Zapatero said.
Mr Blair said "patient determination" was vital for the peace process to succeed.
"There will be ups and downs on the way," he said.
The two men are also said to have discussed tackling illegal immigration into Europe.
The British leader has been credited with helping set up a power-sharing government in Northern Ireland.
The Irish Republican Army announced in 2005 that it had put its weapons "beyond use".
More than 800 people have been killed since Eta took up arms in 1968.