SANAA, Yemen — Airstrikes hit Yemeni government forces heading to the southern port city of Aden to fight separatists backed by the United Arab Emirates on Thursday, killing at least 30 troops, a government commander said.

It was not immediately clear who was behind the airstrikes but the government side blamed the UAE, which has armed and trained separatist militias in southern Yemen.

Officials in the UAE declined to immediately comment.

Infighting has raged for weeks between Yemeni government forces and the separatists, even though the two are allies in a Saudi-led coalition that has been fighting Yemen’s Houthi rebels who control the capital, Sanaa, and most of the country’s north since 2015. The UAE is also part of that coalition.

The fighting between forces loyal to the internationally recognized government and the separatists has added another layer to the complex civil war in the Arab world’s most impoverished country.

Col. Mohamed al-Oban, a commander of the special forces in Abyan province, said the troops were on the road, headed toward Aden on Thursday, when the strikes took place. He didn’t say who carried them out, saying only the planes were from the Saudi-led coalition.

Yemen’s foreign ministry tweeted a statement by Deputy Foreign Minister Mohammed Abdullah al-Hadrami, saying: “The government condemns the Emirati airstrike on government forces.”

“We hold the UAE fully responsible for this explicit extra-judicial targeting” of the government forces, the statement said.

The attack came a day after government forces pushed into Aden to try to retake the city from UAE-backed separatists. Earlier Wednesday, government troops wrested back control of Zinjibar, capital of neighboring Abyan province, from the separatists and headed toward Aden.

Information Minister Moammar al-Iryani said Wednesday that government forces also reclaimed Aden’s airport, the main hub for the country’s south, but the separatists denied that. There were local reports of fighting going on around the airport Thursday.

The push by the government forces into Aden 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.