Iran will surpass the uranium stockpile limit set by its nuclear deal with world powers in the next 10 days, an official said Monday, raising pressure on Europeans trying to save the accord a year after U.S. withdrawal from it lit the fuse for heightened tensions that are now ongoing between Tehran and Washington.

The announcement by Iran's nuclear agency marked yet another deadline set by Tehran. Iranian President Hassan Rouhani already has warned Europe that a new deal needs to be in place by July 7 or the country would increase its enrichment of uranium.

The spokesperson for Iran's nuclear agency, Behrouz Kamalvandi, suggested that Iran's uranium enrichment could reach up to 20 per cent, just a step away from weapons-grade levels.

It appears as if Iran has begun its own maximum pressure campaign on the world after U.S. President Donald Trump's administration reimposed tough economic sanctions that deeply cut into Iran's sale of crude oil abroad and sent its economy into freefall. Europe has so far been unable to offer Iran a way around the U.S. sanctions.

The announcement from Iran on Monday put the U.S. State Department in the position of defending the limits set by the 2015 deal that was so maligned by Trump and his national security team.

"We continue to call on the Iranian regime not to obtain a nuclear weapon, to abide by their commitments to the international community," State Department spokesperson Morgan Ortagus told reporters.

She said Iran's uranium announcement amounted to "extortion" and a "challenge to international norms," as well as to the 2015 agreement known formally as the Joint Comprehensive Plan of Action.

An oil tanker is seen on fire in the Gulf of Oman on Thursday. Two oil tankers near the strategic Strait of Hormuz were reportedly attacked, an assault that left one ablaze and adrift as sailors were evacuated from both vessels and the U.S. navy rushed to assist amid heightened tensions between Washington and Tehran. (ISNA/Associated Press)

The development follows apparent attacks on oil tankers last week in the Strait of Hormuz, assaults that Washington has blamed on Iran, and which Iran has denied being involved in. Iran laid mines in the 1980s targeting oil tankers around the narrow mouth of the Persian Gulf through which a fifth of the world's crude oil passes.

"If this condition continues, there will be no deal" anymore, Kamalvandi said. He accused the Europeans of "killing time" as the clock runs down.

Rouhani, greeting France's new ambassador to Tehran on Monday, similarly warned that time was running out for the deal.

"The current situation is very critical and France and the other parties to the [deal] still have a very limited opportunity to play their historic role for saving the deal," Rouhani said, according to his website.

The announcement appeared timed to strike just as European foreign ministers met in Luxembourg. Federica Mogherini, the European Union's top diplomat, declined to specifically address the Iranian announcement.

"At the moment, as of today, Iran is still technically compliant and we strongly hope, encourage and expect that Iran continues to comply," Mogherini told journalists. She insisted she would await the next report on the issue from the UN's nuclear watchdog, the International Atomic Energy Agency (IAEA).

The heavy water nuclear facility near Arak, Iran, is seen in 2011. (Hamid Foroutan/ISNA via Associated Press)

Under the nuclear deal, Iran can keep a stockpile of no more than 300 kilograms of low-enriched uranium. Kamalvandi said given Iran's recent decision to quadruple its production of low-enriched uranium, it would pass the 300-kilogram limit on June 27.

The Vienna-based IAEA said last month that Iran remained within its stockpile limits and declined to comment Monday on Iran's announcement. Kamalvandi said Iran would continue to allow the UN to inspect its nuclear facilities for the time being.

He also raised the spectre of Iran increasing it enrichment levels, saying the country needs five per cent enrichment for its nuclear power plant in the southern Iranian port of Bushehr and 20 per cent enrichment for a Tehran research reactor, the spokesperson said.

The nuclear deal limits Iran to enriching uranium only to 3.67 per cent, enough for power plants and other peaceful purposes.

But after America pulled out of the nuclear accord and escalated sanctions, Rouhani set a July 7 deadline for Europe to come up with better terms for the deal or Tehran would boost enrichment further. So far, a European mechanism called INSTEX, which is meant to protect trade with Iran, has yet to take off.

Short jump to weapons-grade

The danger, nuclear nonproliferation experts warn, is that at 20 per cent enrichment, only a fraction of atoms need to be removed to enrich up to weapons-grade levels of 90 per cent. Iran maintains its nuclear program is for peaceful purposes, but the 2015 deal grew out of Western concerns about the program.

Israeli Prime Minister Benjamin Netanyahu said the international community should reinstate sanctions if Iran follows through on its threats, adding, "In any case, Israel will not allow Iran to obtain nuclear weapons."

Tensions have ratcheted up in the region since last month. The U.S. rushed an aircraft carrier strike group and other military assets to the Mideast in response to what it said were threats from Iran, and the Pentagon is sending about 1,000 additional troops, officials announced Monday. The deployment includes security forces and troops for additional surveillance and intelligence gathering in the region.

Meanwhile, a series of mysterious attacks have targeted oil tankers and Iranian-backed Houthi rebels in Yemen have launched a series of drone and missile attacks on Saudi Arabia.

Gen. Mohammad Hossein Bagheri, the chief of the general staff of Iran's armed forces, denied Tehran was involved in the tanker attacks, saying Monday the country only would respond in "an open, strong and severe way" if needed.

But he also reiterated Iran's traditional stance on the Strait of Hormuz.

"If we decide to block the Strait of Hormuz, we will to do it in a way that even a drop of oil won't pass the strait," Bagheri said.