Aden: A United Nations conference designed to help forge peace in war-ravaged Yemen has been postponed, a UN official said on Sunday, just four days before it was due to begin.

There had been growing uncertainty over which of the warring Yemeni parties would attend the talks, slated to begin on Thursday in Geneva, and the postponement is a further blow to UN efforts to broker peace in a country where nearly 2,000 people have been killed since March.

“I can confirm that the meeting has been postponed,” the UN official said, without providing further immediate explanation.

Underlining the difficulty of trying to get the rivals around the negotiating table, exiled Yemeni President Abd Rabbo Mansour Hadi laid out his government’s demands to attend the talks in a letter to UN Secretary-General Ban Ki-moon, insisting the Al Houthi militia must withdraw from territory it has seized.

Hadi fled to the Saudi capital Riyadh along with his government in late March when the Iran-backed rebels advanced on his southern stronghold, the port city of Aden.

He reiterated his position on Sunday during talks in Riyadh with the UN special envoy to Yemen, Esmail Ould Shaikh Ahmad.

The embattled leader demanded full implementation of UN Security Council Resolution 2216.

The April resolution called on the Al Houthis to relinquish territory they seized and surrender weapons they took from the army and other state institutions.

The spokesman of the exiled government, Raja Badi, said the resolution “must be implemented in order to bolster the talks.”

“It is difficult for us to attend consultations in Geneva on Thursday under the present circumstances,” he said, before the announcement that the talks had been mothballed.

Al Houthi militiamen and loyalist fighters were locked in fierce fighting on Monday. Clashes raged in the country’s third city Taiz, sowing panic after Al Houthis bombarded several districts with rocket and tank fire.

“There’s a real massacre going on in Taiz, the city that spearheaded the revolt” against former president Ali Abdullah Saleh who now supports the Al Houthis, one resident said.

“Saleh has aligned himself with the rebels to take revenge,” Bassam Al Qadhi added.

More than 545,000 people have been displaced in the Yemeni conflict and although some aid trickled in last week during a five-day ceasefire, people still lack basic needs, including water, electricity and fuel.

A ship carrying 460 tonnes of UAE humanitarian aid docked on Sunday in Aden.

The shipment, including medical and food supplies, is the second from the UAE following the delivery of 1,200 tonnes of aid last week, said local aid coordinator Ali Al Bikri.

Another ship carrying 400 tonnes of diesel also arrived on Friday, said Al Bikri, who was appointed by Yemen’s government-in-exile.

“Aden needs urgently at least 200,000 food rations for the displaced,” Al Bikri added.

Aden has been rocked by fierce fighting between the Al Houthi rebels backed by troops loyal to Saleh and southern fighters allied with the exiled Hadi.

In a bid to restore the authority of Hadi and his government, Saudi Arabia has been leading an air campaign against the Al Houthis since March 26.

The Saudi-led coalition bombarded Al Houthis across the country at the weekend.

Air raids struck several targets in the evening, including the landing strip at Aden airport, and the city’s northern suburbs, officials said.

Strikes by the coalition also hit positions of the pro-Saleh elite Republican Guard in the central province of Taiz, as well as rebel posts in Raymah province, west of the capital Sana’a, witnesses said.

Sources close to the Al Houthis said at least 10 militiamen were killed in the air strikes.

Ten civilians also died and 80 were wounded in shelling of several neighbourhoods of Taiz, Yemen’s third largest city, medics said.

Coalition warplanes circled Sana’a several times on Sunday, prompting rebel forces on the ground to open fire on them with anti-aircraft guns, triggering panic among residents.

Witnesses said a Republican Guard base west of Sana’a was hit three times by coalition raids, after a night in which strikes also targeted arms depots belonging to the rebels southwest of the capital.