President Donald Trump on Wednesday attacked the US intelligence services as "naive" and "wrong" on the threat he says is posed by Iran.

"Perhaps Intelligence should go back to school!" Trump said in a blistering series of tweets.

"The Intelligence people seem to be extremely passive and naive when it comes to the dangers of Iran. They are wrong!" Trump tweeted.

Although especially vehement, it was not the first time Trump has publicly criticised his own intelligence services.

The broadside, which included separate tweets where Trump praised the success of his policies in Syria and North Korea, followed testimony on Tuesday by top intelligence chiefs that were widely seen as contradicting the president's rosy assessments.

In a hearing on global threats at the Senate Intelligence Committee, the top officials took issue with Trump's assertion that the Islamic State (IS) group has been defeated, and that North Korea can be convinced to forego its nuclear weapons.

They also challenged the president's claim that Tehran is actively seeking nuclear weapons, the justification Trump gave for withdrawing last year from a multilateral treaty on Iran.

They underscored again that they believe Russia meddled deeply on Trump's behalf in the 2016 presidential election — which he has repeatedly denied — and can be expected to do the same in 2020.

The hearing took place weeks after Trump cited a victory over IS to justify his sudden announcement of an immediate pullout from Syria, a move that alarmed the US defence establishment and allies in the Middle East.

And it came just weeks before Trump plans a second summit with North Korean leader Kim Jong Un to negotiate a hoped-for denuclearization of the deeply isolated state.