The Spanish government and Eta must return to the negotiating table, Sinn Fein leader Gerry Adams has said.
Eta has been fighting for a Basque state since the late 1960s
Speaking after the Basque separatist group said it was ending its ceasefire, Mr Adams said there was disappointment negotiations had broken down.
Eta said its "permanent" ceasefire would end on Wednesday.
Mr Adams said that both sides had to show "restraint" and that it was important to redouble efforts to resolve the conflict peacefully.
"The lessons of the Irish peace process and indeed every conflict resolution process throughout the world tells us that it is now important to redouble efforts to put the process there back on track," he said.
"All sides should show restraint and do everything in their power to ensure that a process is put in place which can allow this conflict to be resolved peacefully through genuine dialogue and engagement."
Mr Adams visited Madrid and the Basque country last year to urge both sides to develop a peaceful settlement to their long-running dispute, which centres around Eta's pursuit of an independent Basque state.
It was reported in Spain that senior Sinn Fein politicians were involved in the negotiations which led to last year's Eta ceasefire.
Eta declared a "permanent" ceasefire in March 2006, and had insisted it still held, despite a bomb that killed two people at Madrid airport in December.
After the airport attack Spain's Socialist government broke off peace talks.
In a message printed by the Basque newspaper Berria on Tuesday, the banned group said "minimum conditions for continuing a process of negotiations do not exist".
Spanish Prime Minister Jose Luis Rodriguez Zapatero condemned Eta's move.
"Eta's decision goes totally in the opposite direction of the path that Basque and Spanish society want, the path of peace," he said.
ETA's four-decade campaign to achieve independence for the
Basque region of Spain and southwestern France has claimed more than 800 lives.