The head of Nato said on Wednesday that Donald Trump’s renewed strikes on Iran were “absolutely necessary” as the resumption of hostilities threatened to derail a fragile ceasefire agreement.

The US military unleashed a new wave of strikes against Iran on Tuesday and revoked a license allowing Tehran to sell oil after three tankers said they had been struck by projectiles in the Strait of Hormuz.

Speaking ahead of a summit of leaders in Ankara, Nato secretary general Mark Rutte defended the attacks on dozens of Iranian small boats, as Iranian media reported strikes on Kharg Island, Qeshm Island, and in the port cities of Sirik and Bandar Abbas.

“When you have a ceasefire and Iran is basically violating the ceasefire, I think it is totally crucial that the US forcefully react,” Rutte told reporters.

US Central Command defended the strikes, saying that Iran’s “demonstrated aggression was unwarranted, dangerous and a clear violation of the ceasefire”, referring to the three tankers, including a Qatari vessel, that were hit in the strait.

While Tehran denied responsibility for the strikes on ships, Qatar blamed it for attacking the vessels, including its LNG tanker the Al Rekayyat, which reported being hit by a drone that caused a fire in its engine room. The crew were reported safe.

A Saudi-flagged crude oil tanker, believed to be the supertanker Wedyan, was also damaged off Oman, maritime security sources said. The cause was not immediately clear.

The Islamic Republic responded to the renewed US strikes by launching attacks on key US bases in Bahrain and Kuwait, and the IRGC said it had targeted 85 facilities and a reaper drone.

Wednesday’s attacks were the latest threat to a fragile ceasefire agreement since both sides signed a memorandum of understanding in June to end the war and begin 60 days of negotiations aimed a final resolution.

In a potentially major blow to that agreement, Washington moved on Tuesday to withdraw a key concession that had allowed Iran to sell oil on international markets. Oil prices rose more than 3 per cent soon after.

Iran’s foreign ministry condemned the move as a breach of the framework agreement to end the war and said Washington would bear responsibility for the consequences.

A US official said that negotiators continued to work in good faith toward a final agreement with Iran. But control of the strait has given Tehran immense leverage, effectively allowing it to force a stalemate with the world’s most powerful military.

Iran’s clerical rulers aim to install a permanent system to collect fees in what would amount to a huge shift of the balance of power in a region where Washington has long acted as guarantor of security.