(Xinhuanet) -- Russia is concerned over the U.S. announcement on holding negotiations with its European allies to revise the Iran nuclear deal, Russian Deputy Foreign Minister Sergei Ryabkov told reporters.

"These negotiations won't have any effect on our approach towards the nuclear deal and this whole situation ... We will be analyzing it in a most critical way and will continue to judge the events in an unflattering way," Ryabkov said.

He underlined that the deal cannot be amended and that Moscow will "oppose any attempts to hamper it."

The Iran nuclear deal, formally known as the Joint Comprehensive Plan of Action (JCPOA), was signed in 2015 between Iran, and the P5+1 - Russia, France, China, Britain, the United States, plus Germany.

U.S. President Donald Trump on Friday said he will extend sanctions relief on Iran under the nuclear deal for the last time, threatening a U.S. withdrawal from the pact if the U.S. Congress and his European allies can not fix the alleged "disastrous flaws."

Chairman of Russian Federation Council's Foreign Affairs Committee Konstantin Kosachyov slamed the U.S. attempt to review the JCPOA as a dangerous violation of international law.

"Any attempts by the U.S. side to unseal the JCPOA without consent from all the other parties would directly violate the fundamental principles of international law, and as the matter also concerns the nonproliferation regime, it would also serve as a powerful incentive toward its further erosion," Kosachyov said.

Trump's latest move casts doubt on the future of the Iran nuclear deal, a successful practice of solving a hotspot issue through political and diplomatic means.

Iran's Foreign Ministry said on Saturday that Iran will never renegotiate the 2015 nuclear deal despite the U.S. pressure.