Meanwhile, Israeli Prime Minister Benjamin Netanyahu, who was a staunch opponent of the nuclear pact, called for global sanctions to be reimposed immediately "should Iran deliver on its current threats".
A series of more intrusive United Nations inspections under the deal have verified that Iran has been meeting its commitments.
Tensions between Iran and the United States are rising more than a year after President Donald Trump announced Washington was withdrawing from the nuclear deal. "The regime's nuclear blackmail must be met with increased worldwide pressure", he said.
Speaking to reporters at the Khandab heavy water facilities at the Arak nuclear site on Monday, Kamalvandi announced a further halt to certain commitments of Iran under the 2015 nuclear deal, including plans for an unlimited rise in the stockpile of enriched uranium.
"As long as they comply by their commitments, these will go back", Kamalvandi said during a televised press conference at the country's Arak nuclear plant.
In an announcement drawing signs of Western unease, Iran's Atomic Energy Organization spokesman Behrouz Kamalvandi said "We have quadrupled the rate of enrichment (of uranium) and even increased it more recently, so that in 10 days it will bypass the 300 kg limit".
Iran also set a July 7 date for European powers to come up with an agreement to save the deal, or it would move away from the agreement, likely meaning it would increase enrichment further.
Britain said if Iran exceeded the nuclear limits it would consider "all options".More news: Fortnite Fortbyte #49 Location: Found in Trog's Ice Cave Guide
More news: LA Trades For Anthony Davis And Where They Go From Here
More news: Adele parties with the Spice Girls after their final reunion show
The spokesman pointed out that the other signatories still have some time as Iranian nuclear bodies are waiting on the government's decision on the next stage of its obligations reduction under the JCPOA.
When uranium is mined, it typically has about 140 atoms of an unwanted isotope for every atom of U-235. "Weapons-grade" uranium is 90 percent enriched or more.
The owner of the Japanese vessel has also challenged the USA assertions, saying the explosions were caused by some sort of projectile, not the kinds of limpet mines that US military officials believe Iranian agents employed. In fact, the European signatories have already created a financial mechanism called Instex that aims to enable trade with Iran while evading US sanctions - although, per the Atlantic, the USA has threatened to sanction Instex too.
The United States and the IAEA believe Iran had a nuclear weapons program that it abandoned.
Iranian leaders deny any involvement in the attacks on the ships, with a local official responsible for Iranian maritime safety saying both of them appeared to suffer from independent technical issues.
The announcement indicated Iran's determination to break from the landmark 2015 accord, which has steadily unraveled since the Trump administration pulled the United States out of the deal previous year and re-imposed tough economic sanctions on Iran, sending its economy into freefall.
China's Foreign Ministry did not immediately respond to a request for comment.