By Parisa Hafezi and Steve Holland
DUBAI/WASHINGTON (Reuters) - Iran said on Monday it would soon breach limits on how much enriched uranium it can stockpile under a 2015 agreement rejected by the United States, in a new point of contention with Washington which accused Tehran of "nuclear blackmail."
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.
Fears of a confrontation increased last Thursday when two oil tankers in the Gulf were attacked, which the United States has blamed on Tehran. The U.S. military on Monday released images that it says show Iran's Revolutionary Guard removing an unexploded limpet mine from one of the tankers.
The 2015 accord, which Iran and the other signatories have maintained following Trump's decision, caps Iran's stock of low-enriched uranium at 300 kg enriched to 3.67 percent.
But Iran's Atomic Energy Organization spokesman Behrouz Kamalvandi said on Monday: "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's reserves are every day increasing at a more rapid rate," he told state TV, adding that "the move will be reversed once other parties fulfil their commitments."
The move further undermines the nuclear pact also signed by Russia, Britain, Germany, China and the European Union, but Iranian President Hassan Rouhani said the collapse of the deal would not be in the interests of the region or the world.
A White House National Security Council spokesman said Iran's plan amounted to "nuclear blackmail" and must be met with increased international pressure.
The nuclear deal seeks to head off any pathway to an Iranian nuclear bomb in return for the removal of most international sanctions.
Britain said if Iran breached agreed limits then London would look at "all options."
Israel, Iran's arch foe, urged world powers to step up sanctions against Tehran swiftly should it exceed the enriched uranium limit.
However, European Union foreign policy chief Federica Mogherini said the EU would only react to any breach if the International Atomic Energy Agency formally identified one.
GULF TANKERS
Trump's administration has accused Iran of being behind the explosions on tankers in the Gulf of Oman, a vital oil shipping route.
Iran's armed forces chief of staff, Major General Mohammad Baqeri, on Monday denied Tehran was behind the attacks and said if the Islamic Republic decided to block the strategic Strait of Hormuz shipping lane it would do so publicly.
The secretary of Iran's Supreme National Security Council, Ali Shamkhani, said Tehran was responsible for security in the Gulf and urged U.S. forces to leave the region, state TV said.
U.S. Secretary of State Mike Pompeo has spoken to officials from the North Atlantic Treaty Organization, China, Kuwait, South Korea, Britain and other countries to share evidence of Iran's involvement in the attacks on the Norwegian and Japanese tankers, a senior State Department official said.
Iran on Monday accused its main regional rival Saudi Arabia - a close U.S. ally - of adopting a "militaristic, crisis-based approach" for accusing Tehran of carrying out the tanker attacks.
In May, Tehran said it would reduce compliance with the nuclear pact in protest at the U.S. decision to unilaterally pull out of the agreement and reimpose sanctions.
The accord requires Iran to curb its uranium enrichment capacity, capping Iran’s stock of low-enriched uranium at 300 kg of uranium hexafluoride enriched to 3.67 percent or its equivalent for 15 years. That is far below the 90 percent needed for weapons grade uranium and also below the 20 percent level to which Iran enriched uranium before the deal.
A series of U.N. inspections under the deal have verified that Iran has been meeting its commitments.
Iran's Rouhani said on Monday that European nations still had time to save the accord.
"It's a crucial moment, and France can still work with other signatories of the deal and play an historic role to save the deal in this very short time," Rouhani was quoted as saying during a meeting with France's new ambassador in Iran.
French President Emmanuel Macron said he regretted Iran's announcement but that Paris would hold talks with Iran and its partners to avoid any further escalation in the region.
NUCLEAR REACTOR
Kamalvandi, in a news conference at Iran's Arak heavy water nuclear reactor which has been reconfigured under the deal, said Tehran could rebuild the underground facility to make it functional. Heavy water can be employed in reactors to produce plutonium, a fuel used in nuclear warheads.
In January, Iran's nuclear chief Ali Akbar Salehi told state TV that "despite pouring concrete in pipes within the core of the Arak reactor ... Iran had purchased pipes for replacement in case the West violated the deal."
The United States and the IAEA believe Iran had a nuclear weapons programme that it abandoned. Tehran denies ever having had one.
Pompeo said on Sunday the United States did not want to go to war with Iran but would take every action necessary, including diplomacy, to guarantee safe navigation through Middle East shipping lanes.