Saudi-led warplanes launched more deadly strikes in Yemen Thursday despite a demand by Iran-backed rebels for a complete halt to the raids as a condition for UN-sponsored peace talks.

The military coalition has declared an end to the first phase of its operations against the Huthi Shiite rebels and their allies, but vowed to keep hitting them with targeted bombings when necessary.

Two days on, a new wave of strikes killed at least 23 rebels as the World Health Organization said the overall death toll from fighting in Yemen since late March topped 1,000.

Meanwhile, UN Secretary General Ban Ki-moon announced plans to appoint Mauritanian diplomat Ismail Ould Cheikh Ahmed as his new envoy to the country.

He replaces Morocco's Jamal Benomar, who resigned last week after losing support for his mediation efforts from oil-rich Gulf countries.

Saudi Arabia and its Arab allies launched the air war on March 26 in an attempt to restore the authority of President Abedrabbo Mansour Hadi, who was forced to flee abroad last month as the rebels swept across the country.

After the end of Operation Decisive Storm, the coalition said the campaign would enter a phase dubbed Renewal of Hope focusing on political efforts, aid deliveries and "fighting terrorism".

But the Saudi ambassador to the US, Adel al-Jubeir, has since warned that the Huthis should be "under no illusion" that the coalition would refrain from using force "in order to stop them taking over Yemen by aggressive actions".

His remarks came as US President Barack Obama called on Iran to help find a political solution in Yemen, accusing the Islamic republic of contributing to the conflict.

Later on Thursday US defence officials said a controversial Iranian ship convoy suspected of carrying weapons to Huthi rebels had in fact turned around and headed north.

The nine-ship Iranian convoy was "no longer on the same course" and was now south of Salalah, Oman, they said.

Yemeni Foreign Minister Riyadh Yassin had accused Iran of trying to break the coalition naval blockade on his country, in a war he described as an "Iranian plot implemented by the Huthi militia."

The UN Security Council earlier this month imposed an arms embargo on the Huthi forces in Yemen.

- Rebels demand talks -

The Saudi-led alliance says it has destroyed the Huthis' missile and air capabilities, but the rebels still control Sanaa and swathes of the country while Hadi remains in self-exile in Riyadh.

The rebels have called for a complete halt to the raids so warring parties can return to the negotiating table.

"We demand, after a complete end to the aggression against Yemen and the lifting of the blockade, to resume political dialogue... under the sponsorship of the United Nations," said spokesman Mohammed Abdulsalam.

In Yemen's third city of Taez, a Red Cross official said his team had retrieved the bodies of 10 loyalist troops thought to have been killed two days ago when rebels overran their base.

There were more bodies, he said, but the Huthis had denied rescuers access to the area.

The discovery came after a night of air raids in Taez that caused an unknown number of casualties, according to a medic.

A pro-Hadi military official said heavy air raids later struck rebel gatherings in the second city of Aden, where deadly clashes raged.

Three raids also hit rebels in the eastern province of Marib, and others targeted a rebel-held air base in the western city of Hodeida.

- 'Catastrophic' humanitarian situation -

A newly announced division of the Islamic State jihadist group -- the "Green Brigade" -- also claimed a bombing in Yarim the day before that it said had killed five rebels.

In Lahj and Daleh, raids flattened five rebel positions in schools and public buildings, pro-Hadi fighters said.

In Aden, warplanes reportedly hit rebel positions as clashes killed six people, including civilians and pro-Hadi militiamen, and wounded 56 others, officials said.

Meanwhile the Bill & Melinda Gates Foundation said it was providing the International Medical Corps with $800,000 (747,000 euros) to deliver emergency relief to Yemen, after the Red Cross warned of a catastrophic humanitarian situation.

In Nairobi, Somali Prime Minister Omar Abdirashid Ali Sharmarke warned that the conflict posed dangers across the Gulf of Aden, where an influx of refugees is stretching scarce resources and Al-Qaeda is eager for support.

In other developments, global oil prices advanced on the back of the renewal of Saudi strikes, stoking new supply concerns due to Yemen's strategic position into the Red Sea for oil tankers.

Yemen is not a major oil-producing country, but its coast forms one side of the Bab el-Mandeb Strait, through which some 4.7 million barrels of oil passes each day on ships headed to or from the Suez Canal.