ADEN, Yemen (AP) — Yemeni government forces clashed with separatists in the southern port city of Aden on Sunday in fighting that left at least eight people dead, as authorities shut down the country’s main airport, fearing wider unrest.

An Associated Press journalist heard heavy gunfire in the Khor Maksar district, while thick black smoke rose in the sky after an airstrike. The fighting spread to other districts, including areas near the presidential palace.

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Witnesses said residents were fleeing the area. Schools and universities were shut down and students were told to stay home. A medical official said at least eight people were killed and 20 soldiers were wounded. All spoke on condition of anonymity because they feared reprisals.

Airport authorities ordered the evacuation of all planes, fearing that could be damaged in the fighting. State-run Yemenia cancelled all flights to and from Aden.

President Abed Rabbo Mansour Hadi’s forces, which have been at war with Shiite rebels known as Houthis since March 2015, had deployed across the city to prevent protests by southerners who want to bring down his government and separate from the Houthi-dominated north.

The protests are being led by Aidarous al-Zubaidi, a former Aden governor backed by the United Arab Emirates. The UAE is a key member of the Saudi-led coalition allied with Hadi’s government, but has had tense relations with the president. Forces known as the Security Belt, who have been trained and armed by the UAE, led the fighting against Hadi’s forces.

On Saturday, the coalition issued a statement calling for “self-restraint” and described the protests as “popular demands to fix government flaws.”

Aden, the seat of Hadi’s government, has seen a sharp deterioration in services amid accusations of corruption and wasting public funds. Hadi supporters blame the coalition, saying it has failed to fulfill promises to rebuild Aden while barring the president, his sons and top commanders from returning to the country.

The tug-of-war between UAE and Hadi has fractured the coalition and contributed to the nearly three-year stalemate with the Houthis, who control the capital, Sanaa, and much of northern Yemen. The war has killed more than 10,000 people and displaced 2 million. The U.N. says it is the world’s worst humanitarian crisis.

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Northern and Southern Yemen were unified in 1990. Southerners have long advocated greater autonomy or outright secession, complaining of domination by the north. But not all separatists have joined forces with al-Zubaidi, and many fear a return of the civil war that raged in South Yemen from 1986 until unification.

“We won’t allow a repeat of the painful past in Aden and we will not allow disturbances,” Prime Minister Ahmed Obaid Bin Daghar warned on his Twitter. “The government won’t be the reason behind it.”

Later in the day, bin Daghar addressed the coalition, saying, “the allies should not accept the liquidation of the legitimacy which hosted the coalition in the fight against Houthis.”