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"They (US administration) have shown wickedness and malicious behaviour with regard to the JCPOA (nuclear deal) and the US regime is truly a vicious devil," Khamenei said, referring to the chain of sanctions by the Donald Trump administration against Iran, Xinhua news agency reported.
During the negotiations with the world powers in 2013-15, "the country's officials reached the conclusion that they should negotiate and ignore some of their rights so that sanctions would be removed," he said.
"However today, we see that despite all agreements and promises and many discussions during the negotiations, the US treats these negotiations and their outcome in a totally oppressive and bullying manner," he was quoted as saying by Press TV.
Khamenei noted that "the Iranian nation is standing firmly and any wrong move by the hegemonic system concerning the JCPOA would receive the Islamic republic's reaction".
On regional issues, he noted that the reasons behind insecurity in the Middle East can be traced to the "wicked and mischievous interventions" by the US.
After years of tension with the West, Iran struck a deal with Britain, China, France, Russia and the US plus Germany in July 2015, under which Iran agreed to limit its uranium-enrichment activities in return for the lifting of western and international sanctions.
The international agreement is facing a serious threat of collapse as tensions mounted between Washington and Tehran recently.