A statement from the Ministry of Foreign Affairs said that the decision "did not take into account the concerns that [the government] transmitted to the United States of America over the past two years" along with the regional authorities in the Azores. It said that it would carry out a "detailed analysis of this decision and all its possible implications".

The Azores regional government was even more scathing, describing the US move as a "slap in the face" for the government in Lisbon.

Earlier, the US ambassador to Portugal, Robert Sherman, said at a conference in Lisbon that the Defense Department intended to gradually reduce the number of Portuguese employees at the base this year, to 400 from 900 people, as US civilian and military staff are cut to 165 from 650. Overall, he said, this and other cuts at facilities in Europe are aimed at saving $35 million (€29.6 million) a year.

Speaking at a gathering of diplomats earlier this week, the foreign minister, Rui Machete, said that bilateral relations could be damaged if there was a negative outcome in the US review of the Lajes base.

In its statement on the announcement, the government said that while the US government had said it was ready to find solutions to mitigate the effects of scaling back its presence in the Azores, "for now, none of the solutions presented constitutes a real alternative that in fact could mitigate the impact of the reduction".

The Lajes base is a major local employer in what is one of Portugal's poorest regions.

The subject is to come up at a meeting in Lisbon in February, under the regular consultations held between the two countries on the Lajes base and other bilateral security issues.