Iran has threatened to increase its uranium stockpile above the limit set by the 2015 nuclear deal in the next 10 days, amid escalating tensions with the United States and so far unsuccessful European efforts to salvage the deal. Iran said it has already sped up its production of the low-enriched uranium used in nuclear power plants.

Iran has denied claims by the Trump administration and others that it is seeking to build a nuclear bomb. But on Monday, June 17, Iran also announced enrichment targets that would put it in the proximity of the levels needed to build a weapon. It was unclear how long Iran would need to reach those targets.

The announcement comes days after the United States accused Iran of attacking tankers in a key waterway, the Gulf of Oman. News of the suspected attacks last Thursday came as Japanese Prime Minister Shinzo Abe - who had offered to mediate between Tehran and Washington - was wrapping up a visit to Iran that yielded no resolution of the tensions.

The backers of the Iran nuclear deal long argued that the agreement was best-positioned to prevent the scenario threatened on Monday. Despite this, President Donald Trump announced his withdrawal from the Obama-era agreement last year. China, Russia and three European nations - Germany, France and Britain - have stuck to it, arguing that while the deal may not be perfect, it is the best possible solution to prevent Iran from building a nuclear bomb.

Iran initially appeared willing to stick to its commitments, despite the U.S. withdrawal from the deal, but has more recently put pressure on the remaining backers of the agreement.

In early May, Iran gave Europe 60 days to comply with a number of conditions to save the deal without U.S. backing. Tehran threatened it would otherwise resume uranium enrichment above the limits agreed in 2015.

Monday's comments to reporters by the spokesman for Iran's nuclear agency, Behrouz Kamalvandi, indicated that efforts to resume the enrichment could begin even sooner than initially threatened.

Under the 2015 nuclear deal, Iran is allowed to enrich uranium only to 3.67 percent, enough for use as fuel in nuclear power plants but far short of the more than 90 percent needed to produce fissile material for a nuclear bomb. The deal also requires Iran to stockpile no more than 300 kilograms (660 pounds) of low-enriched, 3.67 percent uranium.

Kamalvandi said Monday, however, that Iran would pass the stockpile limit on July 27 and that it needs to enrich uranium to 20 percent for use in an old, U.S.-supplied research reactor in Tehran that produces radioisotopes for medical and scientific purposes.

The moves would constitute a blow to E.U. efforts to uphold the 2015 deal, although Iran's supreme leader last week reiterated the country's commitment in the agreement to never build or acquire nuclear weapons.

During a meeting with Philippe Thiébaud, France's ambassador to Tehran, Iranian President Hassan Rouhani suggested on Monday that Europe could still save the deal, according to his website. "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."

But Iran's demands - which reportedly include stepping up oil exports that have plummeted due to U.S. sanctions in recent months - are unlikely to be fully met by Europe. Helping to boost such exports would constitute a major escalation of tensions between Europe and the United States.

Earlier this year, the European Union created a payment channel - INSTEX - which was supposed to facilitate trade with Iran. In creating the mechanism, the E.U. risked a spat with the United States, where officials fear such efforts to bypass the U.S. dollar in international trade could weaken U.S. influence to impose sanctions abroad in the long run.

But INSTEX has been mired in problems, and most European companies have withdrawn from Iran. The payment channel is also not expected to facilitate oil exports, which would leave a key Iranian demand unmet.

After talks with his Iranian counterpart last Monday, German Foreign Minister Heiko Maas acknowledged that the U.S. withdrawal from the Iran deal has annulled some of the biggest economic benefits that Iran was granted in 2015. "We won't achieve a miracle, but we try as best as we can to prevent failure," Maas told reporters.

Monday's announcement by Iran's nuclear agency clarified how long Europe may still have to prevent such a failure: just 10 days.

This article was written by Rick Noack, a reporter for The Washington Post.