SANAA, Yemen (AP) - Yemen's internationally recognised government accused the Emirati air force of attacking its troops on Thursday (Aug 29) as they were heading to the key southern port city of Aden to fight separatists backed by the United Arab Emirates.

The air strikes killed at least 30 government forces, a Yemeni commander said.

The development raises concerns about the future of a Saudi-led coalition that has been fighting Yemen's Houthi rebels since 2015 and adds another complex layer to the civil war that has ravaged the Arab world's most impoverished country.

Infighting has raged for weeks between forces loyal to Yemen's internationally recognised government and the southern separatists, backed by the UAE - all ostensibly allies in the coalition.

Colonel Mohamed al-Oban, a commander of the government's special forces in Abyan province, said the troops were on the road, headed from Abyan towards Aden on Thursday, when the strikes took place, killing at least 30.

He did not say who was behind them, saying only the planes were from the Saudi-led coalition. The UAE also maintains warplanes as part of the coalition.

Officials in the UAE declined to immediately comment.

Yemen's Foreign Ministry tweeted a statement by Deputy Foreign Minister Mohammed Abdullah al-Hadrami saying: "The government condemns the Emirati air strike on government forces."

"We hold the UAE fully responsible for this explicit extra-judicial targeting" of the government forces, the statement said, adding that the air strikes also left several civilians dead but without providing a specific death toll.

In the statement, the Yemeni government also urged the UN Security Council to condemn the attacks.

Yemen's civil war started in 2014 when Shi'ite Houthi rebels overran the capital, Sanaa, and much of the country's north. A Saudi-led coalition of mostly Arab states intervened a year later to try and restore President Mansour Abed Rabbo Hadi to power.

The UAE is part of that coalition but it never fully threw its support behind Hadi, allegedly over his ties to Yemen's Muslim Brotherhood, choosing instead to train and support the separatist militias.

Yemen was split into two countries, the North and South Yemen, during much of the Cold War before unifying in 1990 but a separatist movement has continued in the south.

The Brotherhood is a pan-Arab Islamist movement that has been designated as a terrorist group by several Arab governments, including the UAE.

Though rare, Thursday's air strikes were not the first time the Emirati planes struck government forces in Yemen, said Farea Al-Muslimi, a visiting researcher with London-based Chatham House.

In January 2018, an Apache helicopter belonging to the UAE hit two armoured vehicles carrying government forces near the Aden airport during a similar bout of infighting between Yemen's Hadi government and the separatists.

However, this was the first time the government in an "explicit and irrevocable" statement turned against the UAE, heralding further fractures in the Saudi coalition, Mr Al-Muslimi said.

Thursday's air strikes also underscore the fragile nature of the Saudi-led coalition and could spell its doom, he added.

"This is a natural ending for a coalition that actually never really existed," said Mr Al-Muslimi. "It was based on instant goals and the belief the war in Yemen would be won quickly." Thursday's air strikes came a day after Yemeni government forces pushed into Aden to try and retake the city from the UAE-backed separatists.

Earlier on Wednesday, government troops wrested back control of Zinjibar, the capital of neighbouring Abyan province, from the separatists and headed toward Aden.

Information Minister Moammar al-Iryani said on Wednesday that government forces also reclaimed Aden's airport, the main hub for the country's south, but the separatists denied that.

According to officials speaking on condition of anonymity to discuss the matter with reporters, forces loyal to Mr Hadi gained some ground at the Aden airport complex before the separatists forced them to retreat.

Videos showing separatist militia in control of the airport were posted on social media on Thursday by the Southern Transitional Council, the separatists' commanding body.

The push by the government forces into Aden also underscored the seesaw nature of the fighting.

Only weeks before, the separatists had gained much territory in southern Yemen, pushing government forces out of strategic cities and areas.