Iran's threat comes after mounting economic pressure from the U.S. and heightened tensions between the two countries.
"Unfortunately, we are heading towards a confrontation," Iran's ambassador to the United Kingdom Hamid Baeidinejad said in an interview.
Iran's nuclear agency said Monday that in 10 days, the country will surpass the limits on its uranium stockpile outlined in the nuclear deal unless European countries can provide the economic relief Iran was promised under the deal, known as the Joint Comprehensive Plan of Action, or JCPOA.
The U.S. withdrew from the deal in May 2018, criticizing it as giving Iran a pathway to a nuclear bomb even though it forbids Iran from developing one. Despite that withdrawal, the U.S. blasted Iran's threat to also violate the deal as "nuclear extortion."
"We continue to call on the Iranian regime not to obtain a nuclear weapon, to abide by their commitments to the international community," said State Department spokesperson Morgan Ortagus on Monday. She declined to answer questions on whether the limits spelled out in the JCPOA are good, instead citing the announcement as an example of "why the president has often said that the JCPOA needs to be replaced with a new and better deal."
A new and better deal seems further away then ever. Instead of driving Iran to the negotiating table, the Trump administration's maximum pressure campaign has seen the country lash out repeatedly. Last Thursday, two oil vessels in the Gulf of Oman were attacked in what the U.S. said was an operation by Iran's Islamic Revolutionary Guard Corps -- which Iran has denied.
Hours earlier, the country's Supreme Leader Ayatollah Khamenei rejected an offer by President Donald Trump to talk, with the president later responding that both sides were "not ready" to meet.
Monday's threat to increase enrichment was a sign Iran "seems to be keen on expanding their nuclear program," warned Ortagus, saying the U.S. was "not surprised" by the announcement.
European leaders have not responded to Iran's ultimatum, but they have been working to create a special economic mechanism to allow companies to work inside Iran and evade U.S. sanctions. That mechanism is said to be online soon, but it's unclear how many companies will risk U.S. economic penalties, with dozens of European firms already leaving Iran.
Instead of allowing any economic relief, the U.S. vowed to increase the pressure on Monday.
"There should be no relieving of sanctions for their malign and unacceptable behavior," Ortagus said.
Pompeo will meet with CENTCOM and Special Operations Command at MacDill Air Force Base in Florida on Tuesday to "discuss regional security concerns and ongoing operations," according to Ortagus, after calling several world leaders over the weekend to discuss America's evidence that Iran was behind last week's attacks.
On Saturday, Pompeo spoke to China's highest-ranking diplomat, Politburo member Yang Jiechi, and NATO Secretary-General Jens Stoltenberg. On Sunday, Pompeo called the foreign ministers of Singapore, Kuwait, the United Kingdom, the United Arab Emirates and South Korea. He called Qatar's foreign minister on Monday morning.
Important on that list are countries reliant on shipping or the oil that passes through the waters off Iran's coast, especially China, Singapore and South Korea. But among those that Pompeo hasn't called are allies that have publicly expressed skepticism about the U.S. claim that Iran is responsible for the attacks, including Germany and Japan.
Despite those public doubts, Ortagus said the U.S. is not disappointed in allies' response.
"We have seen the international community and our allies step up to condemn this behavior," Ortagus said. "We have worked incredibly hard with our allies on this assessment."