British Foreign Secretary Boris Johnson said on Monday that Gibraltar’s sovereignty can only be changed by the territory’s people and UK citizens.

There will be no change to Gibraltar’s sovereignty without Britain’s consent, he declared as the enclave becomes an issue in Brexit negotiations.

His Dutch counterpart, Bert Koenders, meanwhile called for calm after a British politician raised talk of defending the outpost.

“The sovereignty of Gibraltar is unchanged and is not going to change, and cannot conceivably change without the express support and consent of the people of Gibraltar and the United Kingdom, and that is not is going to change,” Johnson said on arrival at a meeting of EU foreign ministers in Luxembourg.

Britain’s departure from the European Union, likely in 2019, is not on the agenda.

A former leader of Prime Minister Theresa May’s Conservative party said she would even be prepared to go to war to defend the territory, as then prime minister Margaret Thatcher did with Argentina over the Falkland Islands 35 years ago.

Asked by reporters if Gibraltar could become a military issue, Koenders urged everyone to keep their cool in Britain’s exit negotiations from the EU.

“You can now see how difficult the divorce is,” he said. “Let us be cool and carry on and not use too harsh language. Let us negotiate, I think that’s the most important.”

Spanish Foreign Minister Alfonso Dastis told Sunday’s El Pais newspaper that Madrid insists it should get a veto over any agreements regarding the strategic enclave on Spain’s southern tip, as Britain prepares to leave.