The US military says it has launched new strikes on southern Iran, targeting Iranian missile sites and boats attempting to place mines.

US Central Command said in a statement the strikes were taken in "self-defense", and were designed "to protect our troops from threats posed by Iranian forces".

Central Command spokesperson Capt Tim Hawkins said the US military "continues to defend our forces while using restraint during the ongoing ceasefire".

The strikes come as Iranian foreign ministry spokesman Esmail Baqai said some progress has made in talks with the US, but a deal to end the conflict "is not imminent".

Hawkins said the strikes targeted an area near Bandar Abbas, a southern port city and home of an Iranian naval base that sits on the Strait of Hormuz, according to the New York Times.

Iranian state media had earlier reported that local officials in Bandar Abbas were investigating after explosions were heard.

Iran is yet to respond to the latest US strikes. It is unclear what impact they will have on any potential peace agreement between the US and Iran.

At the weekend, President Donald Trump had suggested the sides were close to a deal, but later said he had instructed negotiators "not to rush into" one.

US Secretary of State Marco Rubio also said an agreement could possibly be reached on Monday. 

But Baqai responded: "It is correct to say that we have reached a conclusion on a large portion of the issues under discussion... But to say that this means the signing of an agreement is imminent - no-one can make such a claim."

Despite the downplaying of any breakthrough from senior officials, Iran's top negotiator and foreign minister were in Doha for talks with Qatar's prime minister on a potential deal with the US, Reuters reported.

US and Iranian forces have observed a ceasefire since 8 April. Iran has maintained controls on Gulf shipping through the Strait of Hormuz and the US Navy has sought to blockade Iran's ports.

The US and Israel launched wide-ranging strikes on Iran on 28 February, sparking conflict across the Middle East. Iran responded by attacking Israel and US-allied states in the Gulf, and effectively closed the Strait of Hormuz. The move sent oil prices soaring globally.