At least 20 people were killed in an attack on Aden’s airport on Wednesday moments after an aircraft carrying Yemen’s new government landed in the southern city.

Maeen Abdulmalik Saeed, Yemen’s prime minister, who was on the plane, said all members of his cabinet were “fine”. According to the Twitter account of Yemen’s armed forces, he called the incident “part of the war that is being waged against the Yemeni state and its great people”.

The attack, which came as cabinet members returned to the administrative capital in a new power-sharing government formed after a Saudi-led mediation effort, threatens to escalate the fighting in Yemen’s near six-year civil conflict.

Video footage broadcast by Al Arabiya, a Saudi TV channel, showed the government delegation beginning to disembark from a plane when the first blast was heard. Gunfire then erupted as black smoke billowed out of airport buildings. There were later unconfirmed reports of a blast near a presidential palace in Aden where cabinet members had gathered.

The Associated Press put the death toll at 22 people and said dozens were wounded.

No group claimed responsibility for the assault, but officials in the Saudi-backed administration blamed Houthi rebels.

The International Committee of the Red Cross said in a statement that three of its staff were killed in Wednesday’s attack and three wounded.

Yemen has been locked in a devastating civil war since the Houthis, an Islamist movement, seized Sana’a, the capital, in late 2014 and forced President Abd-Rabbu Mansour Hadi into exile.

Saudi Arabia, the United Arab Emirates and their Arab allies intervened in the conflict in March 2015 to back Mr Hadi’s government in its battle against the Houthis.

Riyadh accuses the Houthi movement, which controls Yemen’s populous north, of being an Iranian proxy stoking conflict on its doorstep.

Saudi Arabia has for months been working to broker a deal to reconcile Mr Hadi’s administration with southern secessionists, who are led by the Southern Transitional Council.

The STC, which wants an independent south, has been part of the Saudi-led coalition against the Houthis. But the southern group turned its guns on Mr Hadi’s forces last year and seized control of Aden, threatening to ignite a new conflict within the civil war.

The formation of the new government, which includes STC members, was agreed this month and was designed to ease tensions in the south and remove one of the complexities hindering UN attempts to mediate a nationwide end to the war.

But the attack on the airport underlined the scale of the challenges facing Yemen, which has been ravaged by war and is under the control of numerous armed groups.

Martin Griffiths, the UN envoy to Yemen, condemned the attack. “I wish the Cabinet strength in facing the difficult tasks ahead. This unacceptable act of violence is a tragic reminder of the importance of bringing Yemen urgently back on the path towards peace,” he wrote on Twitter.

The conflict in Yemen has created what the UN describes as the world’s worst man-made humanitarian crisis, with an estimated 14m people, about half the population, on the brink of famine.