The head of the arms control unit at Russia's foreign ministry, Vladimir Yermakov, called on UN members to support the landmark pact with Iran to not "keep silence in hope that the situation will somehow blow over."

Addressing the preliminary review meeting of the Nuclear Non-Proliferation Treaty (NPT), Yermakov described the 2015 Iran nuclear deal as "quite a fragile compromise."

US President Donald Trump has fiercely criticised the complex deal. If he refuses to waive sanctions against Tehran by a May 12 deadline, the accord may unravel.

Russia and China, both supporters of the pact known as the Joint Comprehensive Action Plan (JCPOA), have drafted a statement affirming their "unwavering support for the comprehensive and effective implementation" of the deal.

Yermakov urged all nations at the UN nuclear meet to sign on.

"We believe there is a demand for such a collective message by the (meeting) and hope that the document will find broad support," he said.

The Russian official then took a thinly veiled shot at Trump's call to renegotiate the JCPOA in hopes of getting better terms for the United States.

"Any attempts to amend (the) text for someone's benefit will inevitably... have powerful negative consequences for regional global stability and security," Yermakov said.

His comments came after Russian Foreign Minister Sergei Lavrov vowed in Beijing Monday that China and Russia would block any attempts to "sabotage" the Iran nuclear agreement.

During a first day of discussions on the NPT in Geneva Monday, a long line of speakers had already voiced their support for the Iran deal, including the UN's top representative for disarmament affairs Izumi Nakamitsu.

European leaders are also scrambling the save the deal.

French President Emmanuel Macron is in Washington this week lobbying Trump to preserve the pact, with German Chancellor Angela Merkel due in the US capital on Friday.