The United States' top diplomat on Sunday said Washington still wants to work with Europe to counter Iran's "malign behavior" as President Donald Trump called his withdrawal from the landmark nuclear deal key to containing Tehran.

But while Secretary of State Mike Pompeo talked up the prospect of renewed coordination with America's allies, another top aide reminded Europe its companies could face sanctions if they continue to do business with the Middle Eastern power.

The development came as Iran's foreign minister said he was hopeful of forging a "clear future design" for the pact, while speaking in Beijing at the start of a diplomatic tour aimed at rescuing it.

Trump's announcement last Tuesday that the US was exiting the 2015 nuclear accord was met with widespread dismay among its other signatories -- China, Russia, France, the Britain and Germany.

But Secretary of State Mike Pompeo said Washington was keen to thrash out a more wide-ranging deal with its European partners.

Pompeo, who is barely a fortnight into his new job, told Fox News Sunday that he had been tasked by the president "to work to strike a deal that achieves the outcomes that protect America."

Trump weighed in later Sunday, saying his decision would limit Iran's regional ambitions.

With Pompeo seemingly assuming the "good cop" role on behalf of the Trump administration, it was left to newly appointed US national security advisor John Bolton to remind Europe its firms could be punished if they didn't adhere to American measures.

Zarif embarks on tour
While he has committed to remaining in the nuclear agreement, French President Emmanuel Macron floated the idea of a supplemental deal on Iran during a recent visit to Washington.

Macron and Trump spoke by phone on Saturday, with the US president urging "the need for a comprehensive deal that addresses all aspects of Iran's destabilizing activities in the Middle East," according to a White House readout of the call.

German leader Angela Merkel also told Trump on a visit to Washington late last month that the nuclear deal was insufficient in itself to curb Iran's ambitions in the region.

Although most analysts believe the US withdrawal has effectively scuppered the agreement, Iran's foreign minister talked up the prospects of its survival on Sunday while visiting China, another of the signatories.

Iran hardliners fight back
Zarif will later fly to Moscow and Brussels. Tehran's chief diplomat embarked on the tour as regional tensions spiked just days after unprecedented Israeli strikes in Syria which a monitor said killed at least 11 Iranian pro-regime fighters, triggering fears of a broader conflict between the two arch-enemies.

Iranian hardliners -- who have long opposed President Hassan Rouhani's moves to improve ties with the West -- are already mobilizing against the efforts to save the nuclear deal.