Iran accused the United States on Sunday of threatening Russia with new atomic weapons after Washington published a document outlining plans to expand its nuclear capabilities to deter others.
The review of US nuclear policy published on Friday has riled Russia, which viewed the document as confrontational, and raised fears that it could increase the risk of miscalculation between the two world powers.
"The Americans are shamelessly threatening Russia with a new atomic weapon," Iranian President Hassan Rouhani, a pragmatist who opened the way to Tehran's 2015 nuclear deal with world powers including longtime adversary Washington, said in a speech.
"The same people who supposedly believe that using weapons of mass destruction is a crime against humanity ... are talking about new weapons to threaten or use against rivals," he said in his televised address.
Foreign Minister Mohammad Javad Zarif earlier warned in a tweet that the US policy document posed the risk of "bringing humankind closer to annihilation".
The US military has put countering China and Russia, dubbed "revisionist powers", at the centre of a new national defence strategy unveiled earlier this month shifting priorities away from fighting Islamist militants.
By expanding its own low-yield nuclear capability, the United States would deter Russia from using nuclear weapons, according to American officials.
Russia's Foreign Ministry said on Saturday it was very disappointed by the content of the document, which, it said, has a confrontational feel and anti-Russian orientation.
German Foreign Minister Sigmar Gabriel said the US decision showed "the spiral of a new nuclear arms race is already under way" and added that Europe was, much like during the Cold War, especially vulnerable.
"That's why we need to start new initiatives in Europe for arms control and disarmament," Gabriel said in a statement, adding that developing new weapons sent the wrong message and risked triggering an arms race.
Zarif also said in his tweet: "(US President Donald)Trump's obduracy in killing the #JCPOA (Iran's nuclear deal with world powers) stems from the same dangerous imprudence".
Trump gave the Iran nuclear deal, negotiated before he took office, a final reprieve last month but warned European allies and Congress they had to work with him to fix "the disastrous flaws" in the pact or face a US exit.
He said he would waive sanctions against Iran that were lifted as part of the international deal for the last time unless his conditions were met.
The ultimatum put pressure on European Union powers - key backers and parties to the 2015 international agreement to curb Iran's nuclear programme - to satisfy Trump, who wants the pact strengthened with a separate agreement.