The US government has already begun moves to draw down its military presence at the base, on Terceira island, under a plan announced several years ago. Portugal has repeatedly expressed concerns about the impact on the local economy, which has been heavily dependent on the base for decades.

The senator "said that the question would remain on the table," said Santos Silva, "Above all in this essential point: the Lajes base is only instrumental, but more important than that is the awareness that the US and Portugal are two very close allies, who have very close bilateral relations, and that at the heart of this bilateral cooperation are questions of security and defence."

Santos Silva said that he had in the meeting reminded McCain of the role that the Lajes base can play in maritime security and the monitoring of routes in the south and north Atlantic, and that the senator "was very sensitive to those words". He said he had thanked him for his involvement in raising the issue in discussions in Congress, and asking the Defense Department to look again at the decision to draw down troops.

The minister had already raised the issue with the national security advisor of President Donald Trump, General HR McMaster, whom he met on Tuesday. In that meeting, too, he stressed the importance of maritime security in the Atlantic.

Santos Silva said that he was "very agreeably impressed with the fact that General McMaster is completely up to speed with the Portuguese project of setting up a centre of Atlantic investigation in the Azores".