Implementation of the Iran nuclear deal should not be "affected by any changes in the domestic situations" of countries involved, China's foreign minister warned Monday, as US president-elect Donald Trump threatens to abandon it.

The agreement, signed in Vienna in July 2015 and in force since January, was the signature diplomatic breakthrough of Barack Obama's second term. It calls on Tehran to curb its nuclear programme in exchange for sanctions relief from the US and other nations.

Trump has promised to tear up the nuclear deal once in office, calling the agreement under which it was implemented -- the Joint Comprehensive Plan of Action -- the "worst deal ever negotiated".

The agreement's implementation is the "joint responsibility and duty of all parties" and "should not be affected by any changes in the domestic situations of the countries concerned", Chinese foreign minister Wang Yi told a press conference after meeting his Iranian counterpart Mohammad Javad Zarif.

"What is important is to honour commitments and place emphasis on good faith when it comes to differences or possible differences" over the deal, he said.

In another stumbling block for the deal, the US Congress last week voted to renew longstanding sanctions linked to Iran's ballistic missile tests and human rights record. These pre-date the controversy around Iran's nuclear ambitions.

Washington says these 10-year sanctions have nothing to do with the nuclear agreement, but Iran says the continuing restrictions breach its spirit, particularly since they have discouraged international banks from returning to the country.

"We will not allow any party to unilaterally undertake any actions that are in violation of the nuclear agreement," Zarif said.

He also said he spoke with Wang about increased cooperation on energy, transport, science and technology, national defence and counter-terrorism initiatives.

"We have no reservation and no ceiling for our relations with China, because we share common principles and a common agenda for the future of the global system," Zarif said.

President Xi Jinping visited Iran in January on what both foreign ministers hailed as a "historic" visit, signing a series of agreements that aim to build economic ties worth up to $600 billion within the next 10 years. It was the first such trip to Iran by a Chinese president in 14 years.

Beijing has long taken a back seat to other diplomatic players in the Middle East. But analysts say the region is crucial to Xi's signature foreign policy initiative -- known as "One Belt One Road" and touted as a revival of ancient Silk Road trade routes.

China, the world's second-largest economy, also relies heavily on oil and gas from the Middle East.