The UN has postponed peace talks on the escalating Yemen conflict four days ahead of a scheduled conference.

The decision has come after the effectively-exiled Yemeni President Abd-Rabbu Mansour Hadi said he would not participate in the conference unless the Shiite Houthi rebels withdraw from captured territories.

"I can confirm that the meeting has been postponed," a UN official told AFP without divulging further details.

The postponement of the peace talks yet again underscores the complex nature of bringing rival sides to a negotiating platform. The talks, which were scheduled to begin on 28 May, were intended to "restore momentum toward a Yemeni-led political transition process".

The UN-brokered negotiations led by Secretary-General Ban Ki-moon were to take place in Geneva, but it is unclear when the talks will be held.

On Sunday, 24 May, Hadi's side made it clear at a meeting in Riyadh with UN special envoy to Yemen that they would not be able to take part in the talks as the Houthis have not yet pulled back.

"It is difficult for us to attend consultations in Geneva on Thursday under the present circumstances," Hadi's spokesperson Raja Badi told the news agency.

The Yemen conflict, which worsened in March, has already claimed 2,000 lives and left more than half a million displaced.