Iran’s Revolutionary Guard Corps said on Tuesday it reserved the “legitimate and definite” right to retaliate against any ceasefire violations by the U.S., adding that its air defence units had shot down a U.S. MQ-9 drone and fired at a F-35 fighter jet that had entered Iranian airspace, state media reported.

It claims the F-35, the worlds most advanced and lethal fighter jet, was forced to leave its airspace. The IRGC added that it also fired at an RQ4 intelligence collection drone. This comes after the US carried out what it called “self-defence” strikes in southern Iran overnight, threatening a fragile ceasefire between Washington and Tehran.

The strikes hit coastal towns near ​the Strait of Hormuz which remains closed as peace negotiations continue. Targets also included missile launch sites and and Iranian mine-laying boats.

The key waterway has been closed for almost three months as part of Iran’s retaliation to joint US-Israeli strikes on several of its key sites. The US responded by blocking Iranian ports in the strait.

“U.S. forces conducted self-defense strikes in southern Iran today to protect our troops from threats posed by Iranian forces,” CENTCOM spokesperson Tim Hawkins told the media Monday evening.

The captain added: “Targets included missile launch sites and Iranian boats attempting to emplace mines.

“U.S. Central Command continues to defend our forces while using restraint during the ongoing ceasefire.”

Following the sudden esculation the US secretary of state Marco Rubio said that the Strait of Hormuz has to be open “one way or the other”, adding that the negotiating language of the deal with Iran could “take a few days”.

He called the waterways closure as “unlawful” and “illegal” adding that it “is unsustainable for the world”.

“There were some talks going on in Qatar today, so we’ll see if we can make progress. I think it’s a lot of talking back and forth going on about specific language in the initial document,” Rubio told reporters in Jaipur during an official visit to India.