China and Iran said they will strengthen cooperation to implement the Iran nuclear deal and uphold multilateralism, as Iranian Foreign Minister Mohammad Javad Zarif visited China for the fourth time in 2019.

When meeting Zarif in Beijing on Tuesday, State Councilor and Foreign Minister Wang Yi said the deal faces serious challenges, and the root cause of tensions is that the United States withdrew unilaterally from the deal, gave up its due international obligations and applied maximum pressure on Iran.

The deal, which has been endorsed by a United Nations Security Council resolution, is an important outcome of multilateral diplomacy, Wang said, adding that to maintain its authority and validity is to maintain multilateralism, international law and basic norms that guide international relations.

China supports all kinds of constructive efforts that help ease tensions and uphold the deal, and hopes parties involved will continue to implement the deal effectively by sticking to the right direction, standing up against external pressure and settling differences through talks, Wang said.

Also, China will firmly safeguard international fairness and justice, oppose any kind of unilateral behavior or bullying, and work for political and diplomatic resolutions to the Iran nuclear issue, Wang added.

Wang said he hopes to work with Zarif to implement the consensus reached by the top leaders of China and Iran, and consolidate political mutual trust and deepen pragmatic cooperation between the two countries.

Zarif praised China's role in maintaining the Iran nuclear deal, and briefed Wang on Iran's talks with Russia and Europe over the Iran nuclear issue.

Iran hopes to keep close contact with China to uphold multilateralism, oppose unilateralism and take effective measures to safeguard the deal as well as its own legitimate interests, Zarif said, adding that Iran greatly values its ties with China.

The meeting came after China, Russia and Iran started a joint military exercise in the Gulf of Oman on Friday. The exercise lasted until Monday.

Tensions in the Persian Gulf region have risen since the US announced in May 2018 it was withdrawing from the Iran nuclear deal and reimposing sanctions on Iran, in spite of opposition from the other parties to the deal－Iran, China, France, Germany, Russia and Britain.