"Proposals have been put forward and conveyed to us by the mediators. We have received them, but please excuse me from going into their details," Foreign Ministry spokesperson Esmail Baghaei said during a briefing.

He said Iran's diplomatic team remained active and that proposals from several mediators had reached Tehran. Baghaei dismissed statements from the United States claiming it remained open to diplomacy.

"We have seen and tested their so-called readiness before," he said.

"When the U.S. talks about diplomacy, it actually means dictation, intimidation, threats and sanctions."

Baghaei said Iran would continue defending its dignity and national sovereignty as long as Washington sought to impose its demands.

When asked about reports that the United States could launch a ground operation to seize Khargh Island, the terminal through which Iran exports most of its oil, Baghaei warned of consequences.

“I think there are people in those regions (southern Iran), and their number is not small, and they are looking forward to welcoming those guys (U.S. troops),” he said.

US President Donald Trump had previously threatened to seize the island.

 Baghaei also said Iran repeatedly urged neighbouring countries not to allow the United States to use their territory and facilities to launch attacks.

“What we are doing is self-defense,” he said. “As long as these crimes and military aggression against Iran continue, our armed forces will continue to respond.”

The United States carried out another round of airstrikes early Monday, targeting an area near a northwestern city believed to contain underground missile bases. The attacks followed the announcement of the death of another American service member.

Iran responded by launching attacks on Bahrain, home to the US Navy's Fifth Fleet, and Kuwait.

The latest strikes brought both sides closer to a full-scale war after last month's interim agreement, which was intended to end the fighting permanently, collapsed. Shipping traffic through the Strait of Hormuz also largely came to a halt, while both sides targeted civilian infrastructure used by millions of people.