Iran's President Hassan Rouhani said Thursday that radical talk from critics of the country's nuclear deal with world powers was dangerous and he urged more, not less, diplomacy and dialogue.

His comments came just days after a speech by the commander of the elite Revolutionary Guards, who said the accord, which lifted international sanctions on Iran, amounted to a humiliation.

Rouhani, a moderate cleric under Iran's theocratic system, was boosted in February elections when his allies made gains in parliament and their conservative rivals lost dozens of seats.

However, the polls have been followed by gestures from hardliners within the regime that appear aimed at preventing the nuclear agreement leading to any wider rapprochement.

A flurry of ballistic missile tests conducted by the Guards since October last year triggered fresh US sanctions after a UN panel said they breached previous resolutions.

The tests, however, do not amount to an infringement of the July nuclear accord as it did not cover ballistic missiles.

Rouhani, in a speech broadcast live from Tehran, said the nuclear deal, finally implemented in January after more than two years of talks, showed "logic and argument can triumph over hard power and threats."

"Under radical thinking, there should never be cooperation with the IAEA or the United Nations," Rouhani said, referring to the International Atomic Energy Agency responsible for monitoring the deal.

"Radical thinking tells us not to trust anyone, not to trust neighbours or friends, but moderate thinking tells us... we should talk to the world and seek self-reliance at the same time.

"Being radical is disadvantageous to us everywhere. It creates the biggest danger for any society."

- Once-only opportunity -

The Guards report not to Rouhani but to supreme leader Ayatollah Ali Khamenei, Iran's ultimate authority.

The force's commander, Major General Mohammad Ali Jafari, said on Tuesday that the nuclear deal should not be seen as a model for rapprochement.

If it is "portrayed as a model, that is a sign of narrow mindedness and self-humiliation," Jafari told fellow commanders.

He said that those in Iran who espoused the deal as a model for domestic reconciliation were "involuntarily taking the road to counter-revolution and want to humiliate our great people".

Rouhani has praised the accord, which defused a 13-year showdown with the West, as an example to be followed for forging "understanding and reconciliation" at home.

But he warned the economic opportunities opened up by the deal were "not permanent or ever-lasting."

"If, God forbid, a few people succeed and don't let us use this opportunity well, this opportunity will not be repeated," he said to loud applause, denouncing those who "sow fear and reap fear."

"Uttering hollow and tough words is not art," he said, as Iran prepares to marks its National Day of Nuclear Technology on Friday.

February's elections dealt a severe blow to hardliners -- conservatives who had talked down the nuclear deal in parliament lost their seats.

In contrast, reformists, who want social and political change in Iran, made significant advances as part of a coalition with Rouhani's moderate allies, an outcome seen as an endorsement of the president.

Iran has always denied seeking an atomic bomb.