STATE DEPARTMENT - VOA's Ken Bredemeier and Chris Hannas contributed to this report.
The United States calls Iran's plan to surpass the internationally agreed limit on its stock of low-enriched uranium "nuclear blackmail."
"President [Donald] Trump has made it clear that he will never allow Iran to develop nuclear weapons. The regime's nuclear blackmail must be met with increased international pressure," said White House National Security Council spokesperson Garrett Marquis.
At the State Department, senior officials urged the international community not to yield to the "nuclear extortion" by Iran.
"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 during a briefing, adding that Iran's announcement is "unfortunate" but not surprising.
The U.S. government's comments followed Tehran's announcement Monday that the country would soon surpass the limit on the amount of enriched uranium it is allowed to keep under the 2015 international agreement aimed at restraining its nuclear weapons program.
French President Emmanuel Macron said he regretted the Iranian announcement, urging Tehran "to behave in a way that is patient and responsible." Britain said if Iran exceeded the nuclear limits, it would consider "all options."
In remarks to reporters carried on state television, agency spokesman Behrouz Kamalvandi said, "Today the countdown to pass the 300 kilograms reserve of enriched uranium has started and in 10 days time [June 27] ... we will pass this limit."
But he said Iran would be open to going back to observing the limit if it gets help from other signatories to the agreement in circumventing U.S. sanctions on its vital oil industry.
Tensions between the U.S. and Iran are escalating more than a year after Trump announced Washington was pulling out of the so-called Joint Comprehensive Plan of Action and would begin re-imposing sanctions on Tehran.
In early May, President Hassan Rouhani said Iran, in retaliation for last year's unilateral U.S. withdrawal from the accord, would stop observing restrictions on its stocks of enriched uranium and heavy water that was agreed to under the 2015 nuclear deal.
Washington then imposed tough new economic sanctions on Tehran in the expressed hope of negotiating a new pact with Tehran. But the United Nations atomic watchdog agency says Iran has continued to meet terms of the 2015 pact. While Washington has pulled out of the deal, the other signatories to the agreement have not.
Iran agreed to limit its nuclear program under the 2015 deal to allay concerns about its alleged work on nuclear weapons, and in return it won relief from economic sanctions that had badly hurt its economy.
But Iran contends that the other nations in the deal have not done enough to maximize the economic benefits of sanctions relief while adhering to the nuclear program limits on both the amount of enriched uranium it can hold as well as the level to which it can enrich the material.
Meanwhile, the U.S. has blamed Iran for attacks on two ships passing through the Strait of Hormuz last week and other attacks in recent weeks in the Mideast, claims Tehran has denied. Washington also declared Iran's elite Revolutionary Guards as a terrorist organization.
The State Department said Secretary of State Mike Pompeo had a number of calls with his counterparts over the weekend on assessment of Iran's actions last week, including NATO Secretary-General Jens Stoltenberg, Chinese top diplomat and politburo member Yang Jiechi, Singaporean Foreign Minister Vivian Balakrishnan, Kuwaiti Foreign Minister Sheikh Sabah Al-Khalid Al-Sabah, British Foreign Secretary Jeremy Hunt, Emirati Foreign Minister Abdullah bin Zayed Al Nahyan, Republic of Korea Foreign Minister Kang Kyung-wha, and Qatari Foreign Minister Sheikh Mohammed bin Abdulrahman Al Thani.