Lavrov and his Iranian counterpart Mohammad Javad Zarif are meeting in Moscow, as Zarif seeks "assurances" from the backers of the deal after the USA pulled out.
Upon his arrival, Mr. Zarif met with his Chinese counterpart Wang Yi.
After the Chinese capital, Zarif will attend talks in Moscow and Brussels with representatives of the pact's other signatories.
But he added: "If the nuclear bargain is always to continue, the passions of those people of Iran must be assured".
Wang also noted that China regards Iran as an important partner within the Belt and Road initiative and would maintain bilateral cooperation with the Middle Eastern nation in various fields.
Iran's conservative opposition is aligning increasingly against the deal.
Following his meeting with Zarif on Sunday, China's foreign minister said Beijing would "work to maintain the [nuclear] deal", state news agency Xinhua reported.
The move suggests that Beijing, unlike the European Union, is determined to maintain normal ties and trade with Iran, despite the U.S. urging foreign companies to wind down their operations in the region.
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After Moscow, Zarif will travel to Brussels on May 15 to hold meetings with the foreign ministers of France, Germany, and Britain, as well as EU Foreign Policy Chief Federica Mogherini to discuss the accord.
Meanwhile US Secretary of State Mike Pompeo said it was "ludicrous" to suggest the US decision to withdraw from the deal spurred a recent escalation in tensions between Israel and Iran, in comments broadcast on Fox News on Sunday.
"China and Iran have comprehensive strategic partnership and are trade partners and these relations still continue", he noted. As President of the Republic, we are ready for all options.
"They have made a decision to pull out, we don't think that is necessarily the right thing to do, given that Iran is in compliance with the JCPOA, so we want to hear a little bit more from Washington about their proposals".
Washington's top diplomat Pompeo later said the USA was looking to thrash out a new wide-ranging deal with Europe "that achieves the outcomes that protect America".
JCPOA was implemented in 2016 after five permanent members of UN Security Council, China, France, Russia, United Kingdom and U.S. plus Germany reached an agreement with Rouhani's government to lift worldwide sanctions imposed on the Islamic Republic in exchange for Tehran to curb its nuclear program.
Boris Johnson will meet French and German counterparts to discuss measures to protect European countries working in Iran against the danger of U.S. sanctions after Donald Trump's withdrawal from the global nuclear deal.