Brussels officials will draw up a plan on how to use the EU’s little-known mutual assistance pact in the event of a foreign attack, as Donald Trump’s criticism of Nato intensifies.

EU leaders have agreed that the European Commission “will prepare a blueprint” on how the bloc will respond if the mutual assistance clause is triggered, according to Nikos Christodoulides, the president of Cyprus, who is hosting the talks.

They discussed the mutual defence clause, article 42.7 of the EU treaty, on Thursday night, before reports emerged that the US was exploring how to suspend Spain from Nato.

Trump, a long-term critic of the transatlantic military alliance, has stepped up his invective at “very disappointing Nato” after European countries refused to get involved in the US-Israeli war on Iran. This month he said he was “absolutely without question” considering withdrawing the US from Nato, pushing the 77-year-old alliance into the worst crisis in its history.

Pedro Sánchez, Spain’s prime minister – who has been the most vociferous European critic of the war in Iran – said on Friday that Spain was a loyal Nato member, while renewing his criticism of “the failure of brute force in the Middle East”.