“Portugal will request the intervention of Brussels in this case," Portugal's environment minister, João Matos Fernandes, said on leaving the meeting with his Spanish counterpart, Isabel García Tejerina, and her colleague, the minister of energy, Álvaro Nadal.

"Since there is a dispute here ... it must be resolved” by the commission, he said.

Portugal's government argues that in planning the waste facility next to the nuclear plant at Almaraz "the cross-border impacts were not assessed" as required under European Union law.

“What is demanded by Portugal is that it is recognised that the European directive on environmental impacts was not observed", Matos Fernandes said. The government in Lisbon has “the very strong expectation that the EU will determine that this assessment of cross-border impacts [should] be done.

The request will be submitted to the commission “in principle next Monday”, he added.

While Spain “has made clear that no decision has been taken” yet about whether the Almaraz plant - which began operating in the early 1980s - will continue functioning beyond 2020, Matos Fernandes said, the waste project has been licensed and construction can start.

An official at Almaraz had told Lusa that construction work on the waste facility has not yet started.

According to the unit, the new facility is to be able to store any radioactive material, even that which results from the de-activation of the plant in 2020, if that goes ahead as planned.

Environmental campaigners in Portugal have said that they suspect the decision to build the waste facility is the first step towards extending the life of the plant beyond 2020.

Portugal has never had any nuclear plants of its own.