IRAN claimed on Sunday that it had struck an unmanned United States vessel trying to enter the Strait of Hormuz.

The US did not immediately confirm the attack, which came a day after Washington said its forces had struck three Iranian oil tankers in response to a missile attack on navy warships.

The US resumed its attacks on Iran last week which sparked retaliatory strikes from Iran, who resumed attacks against US assets in the region.

At least five people were killed earlier in the week during a US bombardment of southern Iran.

Iran’s parliament speaker Ghalibaf said on Sunday that attacks on the country would “meet a faster, heavier and more painful response.”

Insisting Tehran’s responses to US strikes would no longer be “proportionate,” he added that “the Americans have surely realised that the era of ‘proportionate responses’ has come to an end.”

“Our recent operations against aggressor bases were merely a start. If they have not realised it yet, they must understand before it is too late that the rules of the game have changed.”

The Trump administration appears to have adopted a dual-prong approach to the conflict, responding militarily to attacks on the strait while going after foreign financial institutions that handle Iran’s money to paralyse the country’s economy.

There appears to be increasing hardship being inflicted on the Iranian people by US sanctions with increasing power cuts and a shortage of water resources in Tehran.

Iran’s Energy Minister Abbas Aliabadi says efforts are currently aimed at stopping power outages but warned there will be occasions when blackouts cannot be avoided.

Meanwhile, the US, Britain, France and Germany have decided to refer Iran to the UN security council for what they say is Tehran’s failure to comply with its nuclear non-proliferation obligations.

Iran has continually stated that it has no intention of seeking to have a nuclear weapon. Tehran insists that its nuclear programme is solely for domestic energy generation.

The war began with illegal and unprovoked US and Israeli attacks on Iran on February 28. 

But the US has broken ceasefire agreements with Iran at least twice, including a memorandum of understanding agreed in June that would have triggered more detailed technical talks about passage through the Strait of Hormuz as well as Iran’s nuclear programme.