"Iran's latest expansion of its nuclear program will lead to further isolation and sanctions. Nations should restore the longstanding standard of no enrichment for Iran's nuclear program. Iran's regime, armed with nuclear weapons, would pose an even greater danger to the world," Pompeo said on Sunday in a message posted on Twitter, Efe news reported.
On Sunday, Iran said it would raise its uranium enrichment level beyond the 3.67 per cent level, marking the second violation of the nuclear deal, but Foreign Minister Javad Zarif said the move could be reversed if European countries upheld their commitments.
The 2015 Joint Comprehensive Plan of Action (JCPOA) limited Iranian nuclear activity in exchange for relief from sanctions.
Tensions with Iran have been rising since the United States pulled out of the nuclear deal with Tehran last year and escalated after President Donald Trump ended sanctions exemptions for purchases of Iranian oil in April.
Trump withdrew the US from the JCPOA in 2018 and Iran's supreme leader has said he was not interested in negotiations until and unless Washington returns to the 2015 pact and ends sanctions that are harming the Iranian economy.
Iran and the rest of the signatories - Russia, China, France, Germany, the UK and the European Union - officially remain committed to the JCPOA.
"Today, Iran is taking its second round of remedial steps under Para 36 of the JCPOA," the Iranian foreign minister said. "We reserve the right to continue to exercise legal remedies within JCPOA to protect our interests in the face of US #EconomicTerrorism."
Trump has been a harsh critic of the JCPOA, calling it a bad deal made by his predecessor, Barack Obama, and former Secretary of State John Kerry.
Last Monday, the Vienna-based International Atomic Energy Agency (IAEA) confirmed that Iran had exceeded the limits on its stockpile of uranium, which can be used as fuel in nuclear reactors or to make atomic bombs.
The IAEA, a UN agency, said its inspectors verified that Iran's stockpile of UF6 was larger than allowed.
( With inputs from IANS )