BEIRUT (AFP) - Syrian President Bashar al-Assad on Wednesday (March 30) reiterated his call for a national unity government, as the White House said his inclusion would make any such proposal a "non-starter".

As the two sides appeared deadlocked over the political transition UN chief Ban Ki-moon highlighted the impact of the five-year conflict by urging greater efforts to tackle the country's refugee crisis at a conference in Geneva.

In an interview published Wednesday, Assad told Russia's RIA Novosti state news agency it would be "logical for there to be independent forces, opposition forces and forces loyal to the government represented" in the new authorities.

But he pushed back against opposition demands that it should be put in place without his participation, insisting that the transitional body they are calling for is "illogical and unconstitutional".

"Neither in the Syrian constitution nor in the constitution of any other country in the world is there anything that could be called a transitional body of power," Assad said.

"It is the national unity government that will prepare a new constitution," Assad said.

Talks led by the UN's Syria envoy Staffan de Mistura paused last week with the sides deadlocked over the fate of Assad, whom the opposition insists must leave power before a transitional government is agreed.

Syria's main opposition High Negotiations Committee flatly rejected the demand from Assad for any transitional government to include his regime.

"International resolutions speak of... the formation of a transitional body with full powers, including presidential powers," HNC senior member Asaad al-Zoabi said, adding "Assad should not remain for even one hour after the formation" of this body.

The form of the executive body that would lead Syria until its elections the UN says should be held in 18 months is the main bone of contention between the two sides.

UN Security Council Resolution 2254 vaguely suggests the establishment of a body to head the political transition.

For the regime, this amounts to a government reshuffle in which the opposition is included, but for the opposition it would be a tranitional body with presidential powers and Assad no role.

In a sign of how high the stakes are, the UN chief Ban exhorted a conference in Geneva "to address the biggest refugee and displacement crisis of our time" which has seen an estimated 4.8 million Syrians fleeing their homeland.

"There is no alternative to negotiating a political transition that will lead to a new Syria," Ban said.

Assad has been buoyed after his forces recaptured the ancient city of Palmyra from Islamic State (IS) jihadists over the weekend, in an advanced backed by Russian air strikes and special forces on the ground.

"The Syrian army is determined to liberate every region," Assad said in the interview Wednesday.

"We are being supported in this by our friends - Russian support was central and key in achieving these results." Soldiers on Wednesday were locked in heavy fighting with IS fighters in central Syria as they pressed their offensive following the seizure of the UNESCO world heritage site.

A ceasefire between Damascus and non-jihadist opposition forces has broadly held since February 27, prompting a glimmer of hope that a political solution might be on the horizon in the conflict that has claimed over 270,000 lives.

But the fighting has left vast swathes of the country in ruin and Assad estimated that economic and infrastructure damage to the country "exceeds $200 billion".

The aim of the Geneva conference is to secure relocation pledges within three years for 10 percent of Syria's refugees, or 480,000 people, whom the UN wants moved outside of Syria's immediate neighbours who are currently absorbing an enormous human burden.

Ban said the 480,000 figure was "a relatively small number," compared with those being hosted by Iraq, Jordan, Lebanon and Turkey.

The Geneva meet follows a conference in London in February where nations pledged $11 billion (9.7 billion euros) to help manage one of the largest displacements of people since World War II.

More than one million migrants - about half of them Syrians - reached Europe via the Mediterranean last year, a rate of arrivals that has continued through the first three months of 2016.

Thousands have died making the harrowing journey, often on rickety boats run by people smugglers.

Some European states have temporarily shut borders and called for tough measures to stem the movement of people through the continent.

The British charity Oxfam on Tuesday noted that wealthy countries had so far only resettled 67,100 Syrian refugees - a mere 1.39 per cent of those forced to flee.