WASHINGTON, Jan. 4 (Xinhua) -- The United States on Monday called Iran's decision of enriching uranium to the 20 percent level at its Fordow facility as "nuclear extortion."

"Iran enriching uranium to 20 percent at Fordow is a clear attempt to increase its campaign of nuclear extortion, an attempt that will continue to fail," a State Department spokesperson said in a statement.

"The United States and the international community will continue to look to IAEA (International Atomic Energy Agency) inspectors to report the facts on the ground," it added.

The Atomic Energy Organization of Iran (AEOI) announced late on Monday that the 20-percent enriched uranium had started at its Fordow facility and had reached the stability level.

According to AEOI spokesman Behrouz Kamalvandi, the 20-percent uranium enrichment process was launched on Monday as part of Iran's Strategic Action Plan to Counter Sanctions, which was approved by the parliament in December 2020.

Iranian Foreign Minister Mohammad Javad Zarif tweeted the same day that Iran's action "conforms fully with Para 36 of JCPOA, after years of non-compliance by several other JCPOA participants. Our measures are fully reversible upon FULL compliance by ALL."

The latest move came amid increasing tension between Washington and Tehran. The Pentagon said late Sunday that U.S. aircraft carrier USS Nimitz would remain in the Middle East waters due to "threats from Iran," reversing a previous decision to order the warship back home.

In May 2018, U.S. President Donald Trump pulled his country out of the Iranian nuclear deal, also known as the Joint Comprehensive Plan of Action (JCPOA), and reimposed harsh sanctions against Iran. In response, Tehran has gradually dropped some of its JCPOA commitments since May 2019.