A third of US Republicans believe that President Barack Obama poses a greater threat to the country than Syria's president Assad or Vladimir Putin of Russia, according to a new poll.

In the Reuters/IPSOS poll conducted this month, 2,809 Americans were asked how much of a threat countries, individuals and organisations posed to the US on a scale of one to five, with one signifying no threat and five a high threat.

Of the Republicans polled, 34% said that they viewed Obama as an imminent threat, compared to Putin at 25% and Assad at 3%.

Putin's government has been accused of instigating violent unrest in east Ukraine, and has in recent years stepped up its aggressively anti-Western rhetoric.

Assad's government is believed to have used chlorine gas and barrel bombs to massacre its own citizens during its five year war against rebel groups.

As part of the survey, conducted between March 16 and March 24, 1,083 Democrats and 1,059 Republicans were questioned.

Terrorist groups Islamic State topped the survey with 58%. Al Qaeda scored 43%, proving that jihadist organisations pose an imminent threat to the US.

North Korean dictator Kim Jong Un polled at 34% and Iran's supreme leader Ayatollah Ali Khamenei at 27%.

Of the issues that face America, 39 per cent viewed cyber attacks as an imminent threat, and a third drug trafficking.

Obama has long been criticised in extreme terms by the Republican right.

In the run-up to the 2012 US presidential elections, Republican candidate Newt Gingrich described Obama as "the most dangerous president in history" and argued that defeating him was a "duty of national security".

Recently, Republicans have accused Obama of "appeasement" in seeking a nuclear deal with Iran, with Senators writing to Khamanei to warn that any deal could be undone by the US senate or a future administration, and inviting Israeli prime minister Binyamin Netanyahu to address Congress on the alleged threat posed by the deal.