BRUSSELS - Nato chief Jens Stoltenberg on Friday refused to intervene in the row over the Iran nuclear deal, but said the alliance had concerns about Tehran's "continuous development of missile capabilities".

US President Donald Trump is set to "decertify" the landmark 2015 agreement which curtailed Iran's nuclear programme in return for sanctions relief, leaving lawmakers to decide whether to withdraw completely.

Stoltenberg refused to be drawn on whether he thought the deal was working, but stressed that compliance with its conditions was essential if it was to have any meaning.

"It is not for Nato to make assessments about compliance, that's for nations that are part of the agreement and the IAEA to make that kind of assessment," he told AFP in an interview.

And he reiterated Nato concerns about issues not covered in the deal, in particular Iran's ballistic missile programme.

"The nuclear deal covers the development of nuclear weapons but it doesn't cover missile programmes and we are concerned about the continuous development of missile capabilities of Iran," he said. Trump has derided the agreement as "the worst deal" and accused Tehran of not living up to the "spirit" of it, but UN inspectors say Iran is meeting the technical requirements of its side of the bargain. International allies, particularly the EU, have lobbied for it to stay, arguing that it is effective.

Nato warns against N Korea military action Nato chief Jens Stoltenberg told AFP on Friday that a military intervention against North Korea would have "devastating consequences", after US President Donald Trump said diplomatic efforts had failed. Stoltenberg, who will visit South Korea and Japan in the coming weeks as a show of support, stressed that Washington had the right to defend itself and its allies, but called for greater diplomatic efforts. "The use of military force will have devastating consequences, I think nobody really wants that, therefore we need to continue to push for a negotiated solution," Stoltenberg said in an interview at Nato HQ in Brussels.

"The US has the right to defend itself, to defend its allies, but at same time I am absolutely certain no one wants a military solution, so we still see a united effort to try to step up the pressure against North Korea."

Trump met his national security team on Tuesday and discussed a "range of options" to respond to Pyongyang's repeated recent nuclear and ballistic missile tests.

The meeting came days after Trump, who last month threatened to "destroy" North Korea, said on Twitter that years of talks with Pyongyang had achieved nothing and "only one thing will work".

The United States and South Korea will kick off a major navy drill in the Sea of Japan and the Yellow Sea in a show of force against the North next week and there has been a flurry of military hardware movement in the region in recent days.

Earlier this week two supersonic US heavy bombers flew over the Korean peninsula, staging the first night-time joint aviation exercises with Japan and South Korea, the latest in a series of flyovers.

Stoltenberg stressed that Nato was "not planning any military presence in that part of the world" and no such request had been received from Tokyo or Seoul.

But the growing range and accuracy seen in the North's missile tests has prompted the 29-nation alliance to review its missile defence system, which has been partially operational from a base in Romania since last year.

"Our experts are working on technology, on how to improve our systems," Stoltenberg said.