Tensions escalated in the Gulf region over the weekend as Iran distanced itself from the 2015 nuclear deal amid growing threats and pressure from the United States.

The Iranian cabinet said in a statement on Sunday that the country would "take the final step to reduce commitments to the Joint Comprehensive Plan of Action", and would not observe restrictions in operational areas, including uranium enrichment capacities, enrichment percentage, the volume of enriched material and research.

Teheran will abandon the last key restriction in the operational field put up in the 2015 nuclear deal regarding "the limitations in the number of centrifuges", and will proceed solely based on the country's technical needs, Iran's Islamic Republic News Agency reported.

As an important party to the nuclear deal, China is highly concerned about the current situation in the Middle East, Foreign Ministry spokesman Geng Shuang said on Monday, adding that the region's peace and stability is of vital importance for the entire world.

Geng said that Iran has exercised restraint, although it was forced to end its commitment due to external factors. "Iran has clearly expressed its political willingness to comprehensively and effectively implement the 2015 nuclear deal and does not break obligations as stipulated by the Treaty on the Non-Proliferation of Nuclear Weapons," he said.

Iran's 2015 nuclear accord with the United Kingdom, China, France, Germany, Russia and the US has been hanging by a thread since Washington's unilateral withdrawal in May 2018.

Foreign Ministry spokesman Geng said the withdrawal was "the root cause of the Iran nuclear tensions".

"It should also be the basic starting point for all related parties to deal with the Iran nuclear issue in an objective and fair way," he said.

Iran's announcement was another sign of the fallout from Friday's assassination of senior general Qasem Soleimani in Baghdad in a drone strike ordered by US President Donald Trump.

On Monday, hundreds of thousands of people in Teheran mourned the death of Soleimani, the former commander of the Quds Force of Islamic Revolutionary Guard Corps.

Geng said at a regular news conference in Beijing that the risky military behavior of the US "goes against the basic norms governing international relations as well as aggravates the tensions of the regional situation", and the power politics "are neither popular nor sustainable".

The deadly strike has caused an unexpected stir in Iran and even the entire Persian Gulf region and limits opportunities to resume the suspended talks on the nuclear deal, said Zhu Weilie, director of the Center for China-Arab States Cooperation Forum Studies at Shanghai International Studies University.

Iran's decision indicated the rapid escalation of tensions, and under such circumstances it will be difficult to avoid some regional conflicts, Zhu said.

Meanwhile, Zhu said the announcement also shows Iran's disappointment with European countries.

"The solution of establishing a special payment system led by the European countries has failed to meet Iran's expectation to break the economic blockade caused by US sanctions," he said. "Iran is pressing the Europeans by calling off its commitment to the nuclear deal."

The leaders of Germany, France and the UK reacted by urging Iran to rethink its announcement.

"We call on Iran to withdraw all measures that are not in line with the nuclear agreement," German Chancellor Angela Merkel, French President Emmanuel Macron and British Prime Minister Boris Johnson said in a joint statement.

They also urged Iran to refrain from taking "further violent actions or support for them" and called on all parties involved to "show utmost restraint and responsibility".

"It is crucial now to de-escalate," they said.

Zhu emphasized that although Iran said it reduced its commitments, it still "plays within the frame and hasn't crossed the line".

"We should see that Iran's non-compliance does not mean that it will begin to resume the development and use of nuclear weapons."

Iranian Foreign Minister Mohammad Javad Zarif referred to Iran's final remedial step under the 2015 nuclear deal and said that Iran will continue its cooperation with the International Atomic Energy Agency.

In comments posted on social media, Zarif said the latest step taken by Iran was within the remit of the Joint Comprehensive Plan of Action and "all five steps are reversible upon effective implementation of reciprocal obligations".

The cabinet statement also said Iran will be ready to return to its commitments under the 2015 nuclear deal once the sanctions are removed and the country gets benefits from the agreement.

Meanwhile, Trump insisted on Sunday that Iranian cultural sites were fair game for the US military, dismissing concerns within his own government that doing so could constitute a war crime under international law.

"These media posts will serve as notification to the United States Congress that should Iran strike any US person or target, the United States will quickly and fully strike back, and perhaps in a disproportionate manner," he said on social media.

The president claimed on Saturday that the US had targeted 52 Iranian sites, including cultural sites, and would hit them "very fast and very hard" if Iran retaliates, raising questions about the legality of attacks against significant world heritage sites.

Mo Jingxi, AFP and Reuters contributed to this story.