In statement, the Azores government said that this 35th meeting of the commission will be the fourth attended by Cordeiro.

It is to examine, “among other subjects, the process of downscaling US forces at the Lajes base”, the note states.

In 1995, Portugal and the US signed a cooperation and defence treaty that included a technical agreement regulating the use of the Lajes base and other Portuguese military installations, and an employment agreement regulating Portuguese workers on the base. It is under these provisions that the permanent bilateral commission was set up, to ensure they were executed and to foster cooperation between the two countries.

Its last meeting was in December, in Angra do Heroísmo, on Terceira. Afterwards Cordeiro described it as “productive”, but said that aspects continued to require a lot of work, including environmental questions.

In January 2015 the US defence secretary, Chuck Hagel, announced plans to withdraw 500 US military personnel from the base. Hundreds of civilian jobs are also expected to be lost as a result.

In the wake of that announcement the regional government unveiled an economic revitalisation plan for Terceira to offset the impact of the drawdown, and asked the government in Lisbon to secure from the US government €167 million a year for the island for 15 years to help fund its implementation.

In March this year the Defence Department submitted a report to the US Congress that ruled out the idea of the Lajes base being the site of a new information centre, currently planned for the UK.

In response, Cordeiro argued that “there remains no other alternative except triggering a process of revising the cooperation and defence treaty” between Portugal and the US, as well as the related accords, on the grounds that “the conditions that existed for the signing of the treaty where the US presence are concerned are completely different”, and given that the way that the whole process has been managed “also does not honour the spirit of this treaty."

Last week, during a visit to the Azores, Portugal's prime minister, António Costa, stressed that the matter was not closed as negotiations continue between the two countries on the use of the base, but argued for an alternative scientific uses for the base in the fields of meteorology, volcanology and oceanography.