France warned Monday that salvaging the Iran nuclear deal was "essential," but left the door open to further talks to ward off any US threat to walk away from the landmark agreement.

Foreign Minister Jean-Yves Le Drian told reporters ahead of the UN General Assembly that scrapping the 2015 agreement would launch an arms race with "neighboring countries that would feel encouraged to head into the same direction."

US President Donald Trump has threatened to scrap the nuclear agreement, describing it as the "worst deal ever negotiated."

"France will try to persuade President Trump of the importance of this choice, even if it can be completed by work after 2025," he said ahead of a meeting between Trump and French President Emmanuel Macron later in the day.

Under the nuclear deal, certain limits on Iran's uranium enrichment are set to expire in 2025 and critics have said this is the weakest part of the deal.

"It's essential to maintain (the agreement) to prevent a spiral of proliferation that would encourage hardliners in Iran to pursue nuclear weapons," Le Drian said.

France and the United States are among the six powers that negotiated the landmark agreement with Iran. Britain, China, Germany and Russia are also part of the deal.

Under the nuclear deal, Iran surrendered much of its enriched uranium, dismantled a reactor and submitted nuclear sites to UN inspection, while Washington and Europe lifted some sanctions.

- Iran, North Korea top UN agenda -

Iran and North Korea are set to dominate the annual gathering of world leaders that formally opens on Tuesday with a series of addresses by Trump and Macron among other leaders.

Iranian President Hassan Rouhani is scheduled to speak on Wednesday.

Trump is due to decide before October 15 whether Iran has breached the 2015 nuclear agreement, and critics fear he may abandon an accord they think prevents Tehran from building a nuclear bomb.

US Secretary of State Rex Tillerson will join his Iranian counterpart Mohammad Javad Zarif on Wednesday for a meeting of the so-called E3+3 on the nuclear deal, chaired by the European Union.

Turning to North Korea, Le Drian said that "very strong" pressure from sanctions would compel leader Kim Jong-Un to come to the negotiating table to put an end to his missile and nuclear programs.

"Military action is not required," said the foreign minister.

"To bring North Korea to the negotiating table, the only possible way is to apply very strong pressure," he added.

The UN Security Council last week imposed a new raft on sanctions on North Korea after it carried out its sixth and most powerful nuclear test.

The council will meet Thursday at a ministerial level to discuss ways of enforcing sanctions, which depends largely on cooperation from China, North Korea's largest trading partner.