A Yemeni Shiite Huthi rebel stands next to a national flag in the capital Sanaa on September 21, 2015
Aden (AFP) - President Abedrabbo Mansour Hadi flew in to war-ravaged Yemen's second city Tuesday after six months in exile in Saudi Arabia, vowing to make a rapid return to the rebel-held capital.
Only hours earlier, warplanes from a Saudi-led coalition killed at least 21 people in Sanaa, a day after thousands of sympathisers took to its streets to celebrate a year since its seizure by Iran-backed Shiite Huthi rebels.
Hadi, who is recognised by the international community, arrived in Aden aboard a Saudi military aircraft that landed at an airbase adjoining the civilian airport in the southern port city.
He promised a rapid return to Sanaa.
"The return to the capital Sanaa will come soon after the liberation of all cities and provinces," from the hands of militias, he said in a statement.
In the immediate near term, the presidency said Hadi would remain in Aden for a few days before heading to New York to attend the UN General Assembly.
In New York, UN chief Ban Ki-moon was "extremely concerned by the escalating ground fighting and air strikes that have caused... an ever-growing number of civilian casualties in recent days," his spokesman said.
He reminded all parties of their obligation to "take all feasible precautions to avoid loss of civilian life and damage to civilian objects."
Aden was Hadi's last refuge when he fled the rebel-controlled capital after they took over the government.
Much of the city has been reduced to rubble by months of ferocious fighting, with the rebels backed by renegade soldiers loyal to ousted president Ali Abdullah Saleh.
Prime Minister Khaled Bahah and several ministers returned to Aden last week, two months after it was retaken from the rebels.
The Saudi-led coalition launched air strikes against the rebels on March 26, and began a ground operation in July.
Hadi's return comes ahead of the Muslim holiday of Eid al-Adha, or the Feast of the Sacrifice.
In July, Hadi said "Aden will be the key to Yemen's salvation," in a televised address marking the end of the Muslim fasting month of Ramadan.
Since then, the Huthis have lost five southern provinces to loyalists, who are now waging a major offensive in oil-rich Marib province east of the capital.
The rebels still control much of northern and central Yemen.
- Peace talks collapse -
Hadi loyalists began an all-out offensive against the Huthis in Marib on September 13, aiming to retake the capital.
A day later, Hadi's government backed out of UN-brokered peace talks in Oman after saying only days earlier that it was going to take part.
Hadi's office said the government would not attend talks unless the rebels first accept UN Security Council resolution 2216 demanding their withdrawal from territory they have captured.
Loyalists have also been locked in fierce fighting for control of third city Taez, which is also seen as a crucial gateway to Sanaa.
The United Nations says nearly 4,900 people have been killed since late March in Yemen. The UN aid chief has called the scale of human suffering "almost incomprehensible".
In the latest bloodshed, Saudi-led warplanes killed 21 people Tuesday, including civilians, in a raid targeting Huthis in the Sabeen neighbourhood of Sanaa, a medical official said.
The death toll was likely to rise because some people were missing, another medical source said, as rescuers combed the rubble.
- Drone strike on Qaeda -
Elsewhere, a US drone strike killed two suspected members of Al-Qaeda east of Sanaa, an official said.
"Two members of Al-Qaeda were killed when a missile from a US drone hit their vehicle" on the outskirts of Marib during the night.
The United states has waged a longstanding drone war against Al-Qaeda's Yemen-based branch which it regards as the jihadist network's most dangerous.
The strikes have continued alongside the Saudi-led campaign.
Al-Qaeda said in June that its leader in Yemen, Nasir al-Wuhayshi, had been killed by a US drone.
Al-Qaeda in the Arabian Peninsula controls parts of the vast southeastern province of Hadramawt, including the provincial capital Mukalla, seized in April.
On Monday the jihadists angered Mukalla residents by razing tombs in an old cemetery.
"Some of these tombs are for religious dignitaries and are 300 years old," an official said.
Al-Qaeda and its jihadist rival, the Islamic State group, regard the reverence of tombs as tantamount to idolatry.