Former US president Donald Trump's mould-breaking approach has reshaped decades of Middle East diplomacy, but his legacy in the troubled region has quickly come under attack from his successor.

From unexpected normalisation deals with Israel, to a "maximum pressure" campaign on rival Iran, the businessman-turned-president changed the face of the Middle East.

His close relations with autocratic heads of states and wealthy Gulf monarchies also personalised Washington's approach towards the strategic region which hosts thousands of US troops.

Joe Biden promised to change all that.

In less than 10 days in the White House, the new president has already erased some of his predecessor's signature moves, but analysts say many of the flurry of deals struck in the last weeks of the administration won't -- or shouldn't -- be easily overturned.

Here is a look at what is at stake for Trump's Middle East legacy:

On his first full day on the job, Secretary of State Antony Blinken confirmed the Biden administration wants to return to the 2015 nuclear deal trashed by Trump -- but said it would only happen once Iran resumes its commitments.

Tehran has meanwhile called on Washington to first unconditionally lift sanctions, effectively dismantling the pressure campaign.

Observers say this ping-pong process exemplifies the difficulty in extricating the US from Trump policies.

"The more the administration pursues the Iranians, the more the Iranians will pull back, in a bid to increase their leverage. Yet, the more the US pulls back, the more the Iranians will try to force the US to engage," said Jon B. Alterman from the Center for Strategic and International Studies.

"We should not expect an easy return to negotiations, whatever the Biden team wants, and we should not anticipate that a supposedly wounded Iran will capitulate. Instead, we should anticipate a drawn-out process punctuated by crisis."

In a regional game-changer, the US last year agreed to sell more than $23 billion worth of top-of-the-line F-35 fighter jets and drones to the United Arab Emirates, to reward its diplomatic recognition of Israel.

Trump also backed arms sales to Saudi Arabia, despite lawmakers' objections which were centred on the kingdom's poor human rights record.

The Biden administration has said it is "temporarily" freezing the deals "to allow incoming leadership an opportunity to review".

Experts say a halt would raise questions about a potential impact on the normalisation deal with Israel, which Trump saw as a key foreign policy achievement.

A Palestinian walks past a defaced mural painting of former US president Donald Trump on Israel's controversial separation barrier, which divides the West Bank from Jerusalem
A Palestinian walks past a defaced mural painting of former US president Donald Trump on Israel's controversial separation barrier, which divides the West Bank from Jerusalem AFP / AHMAD GHARABLI

Trump's term saw a flurry of normalisation deals between four Arab states and Israel. Most however were built on diplomatic quid pro quos, which makes them vulnerable in the Biden era.

Morocco's accord struck in December saw the US back its rule over disputed Western Sahara. Despite hailing the peace deals, Biden has not committed to maintaining the recognition in the region, where tensions have simmered since the 1970s.

For its part, Sudan signed the deal less than a month after the US removed it from its "state sponsors of terrorism" blacklist.

The Biden administration should not jeopardise these agreements and should "forge even more", said Dennis Ross and Juan Zarate in an article for the Washington Institute.

"Although the instinct to make dramatic changes is understandable and sometimes correct, certain elements of Trump policy provide good opportunities for furthering Arab-Israel engagement."

After a three-year diplomatic row between a Riyadh-led quartet and Qatar that veered from frosty to furious, Gulf leaders met in Saudi Arabia two weeks before Trump's exit and agreed to restore relations.

Washington had intensified pressure for a resolution, insisting Gulf unity is necessary to isolate Iran.

However, the accelerated agreement failed to address any of the quartet's conditions to restore relations with Doha, which was accused of being too close to Tehran and financing extremists.

As a result, "intra-Gulf rivalries could continue to stoke conflicts and political tensions in the Middle East and Africa," said Elham Fakhro of the International Crisis Group.

Trump's administration designated the Iran-backed Yemen Huthi rebels as a terrorist organisation just one day before Biden's inauguration, a move that raised fears it could jeopardise aid operations and put millions of lives at risk.

Biden's administration on Monday froze the decision for one month.

Blinken said one of his top priorities is addressing the war in Yemen, where US ally Saudi Arabia has been bombarding the Huthis since 2015.

One of Trump's first moves was to ban access to the United States to all travellers from Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen, igniting international outrage and triggering domestic court battles.

On his first day, Biden lifted the measure, enabling many Middle Eastern families to visit their relatives for the first time in four years.