Tehran: Iran's top negotiator Mohammad Bagher Ghalibaf on Sunday warned that Tehran would respond more swiftly and forcefully to any further US attacks, following an Iranian strike targeting an American military vessel in the Strait of Hormuz.

"The Americans must have understood that the era of proportionate responses has come to an end," Ghalibaf said in a speech carried by Iranian state media. He added that "any aggression against Iran's interests and security will receive a faster, more intense and more painful response".

Iran said it had struck an unmanned US military boat in the Strait of Hormuz on Sunday, in the latest escalation between the two countries after around a month of relative calm.

Iranian state media reported that the US vessel was attempting to enter a restricted area in the strategic waterway. US Central Command, which oversees American military operations in the Middle East, did not confirm the claim and did not immediately respond to a request for comment.

The development came a day after the US said it had struck Iranian oil tankers in retaliation for Iran's launch of ballistic missiles at US Navy warships.

Fighting resumed last week following roughly a month of relative quiet. The broader conflict began with US and Israeli attacks on Iran on February 28. Although a ceasefire was announced in June, intermittent hostilities have continued as both sides seek to impose military and economic costs on the other and diplomatic negotiations have faltered.

Meanwhile, Israeli strikes in southern Lebanon killed four people and wounded at least 20 others, including children, according to Lebanese authorities. The strikes took place near an area that has emerged as a flashpoint in the conflict between Israel and Iran-backed militant group Hezbollah.