France on Monday warned that salvaging the Iran nuclear deal was “essential” to prevent other countries from seeking nuclear weapons as world leaders gathered at the United Nations (UN).

Foreign Minister Jean-Yves Le Drian also told reporters ahead of the UN General Assembly that pressure from sanctions, and not military action, was the only way to address the crisis over Pyongyang's nuclear and missile tests.

“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.

The foreign minister said scrapping the 2015 nuclear deal would launch an arms race with “neighbouring countries that would feel encouraged to head into the same direction".

United States (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,” he said ahead of a bilateral meeting between Trump and French President Emmanuel Macron later in the day.

France and the US are among the six powers that negotiated the landmark agreement with Iran. Britain, China, Germany and Russia also approved 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 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.

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 programmes.

“Military action is not required,” the foreign minister reiterated.

“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.