Xi met one-on-one with Iranian counterpart Hassan Rouhani on Sunday following a two-day regional security summit in the eastern Chinese city of Qingdao that also included Russia and former Soviet republics.

President Donald Trump announced last month the US was withdrawing from the 2015 nuclear deal and re-imposing sanctions that would hit international businesses working in the Islamic republic.

The other parties to the deal -- Britain, France, Germany, China and Russia -- have vowed to stay in the accord but their companies risk huge penalties if they keep doing business in Iran.

In his meeting with Rouhani, Xi described the deal as "an important outcome of multilateralism", according to the official Xinhua news service.

Xi said the deal is "conducive to safeguarding peace and stability in the Middle East and the international non-proliferation regime, and should continue to be implemented earnestly," according to Xinhua.

Rouhani said Iran expects the international community, including China, "to play a positive role in properly dealing with relevant issues", the agency reported.

During the summit of the Shanghai Cooperation Organisation (SCO) on Sunday, Russian President Vladimir Putin told the assembled leaders, including Rouhani, that the US withdrawal could "destabilise the situation" but Moscow still supports the "unconditional implementation" of the deal.

Rouhani also had a bilateral meeting with Putin in Qingdao on Saturday and said more talks were needed between their two countries following Washington's "illegal" withdrawal, according to the Kremlin.