The development came after Washington and Tehran accused each other of violating an ongoing truce following an exchange of fire, three months after the conflict began with US-Israeli strikes on the Islamic republic.The sources confirmed reporting by the Axios news outlet that the two sides had reached an agreement on a memorandum of understanding to prolong the truce and launch negotiations on Iran's nuclear programme.The provisional agreement is significant as it arrived just days after the most serious trading of fire since the ceasefire started in April, rattling ongoing diplomatic efforts to end the war.The clash had also drawn in US ally Kuwait, which accused Iran of a "dangerous escalation".US strikes on the southern Iranian port city of Bandar Abbas prompted Iran to target "the American airbase that served as the source of the attack", according to state broadcaster IRIB, citing the country's Revolutionary Guards.The Guards did not specify the location, but Kuwait, which hosts US troops, said its air defences had responded to incoming fire.Its foreign ministry later condemned "the criminal Iranian attacks that targeted the territory of the State of Kuwait with missiles and drones, in a dangerous escalation".The US Central Command called the attack an "egregious ceasefire violation".Iranian forces had fired at four ships attempting to transit the Strait of Hormuz without authorisation, IRIB reported on Thursday. Iran has blockaded the waterway since the war began on February 28.US forces said they had intercepted five attack drones in and around the strait, and prevented the launch of a sixth from a ground control station in the Bandar Abbas area.Iranian foreign ministry spokesman Esmaeil Baqaei said Iran would "take all necessary measures to defend its national sovereignty", likewise describing the US strikes as truce "violations".A US official told AFP the actions had been "measured" and "intended to preserve the ceasefire".Iran's Guards threatened a "firm response" on Thursday in the event of renewed attacks.Hormuz impasseBefore Thursday's strikes, Amir, a 27-year-old software developer in Tehran, said fears of renewed fighting were ever present in spite of the ceasefire and talk of a deal."I feel like nothing is certain yet," he said. "The daily question is: Will there be missile strikes tonight?"