Saudi warplanes targeted separatist fighters in Yemen, killing at least seven in a counterattack against a sweeping advance by the UAE-backed Southern Transition Council.

The deaths are the first from coalition fire since the secessionist STC seized swathes of Hadramawt and Mahra provinces last month.

Following the strikes, a military spokesman for the STC said it was in a “decisive and existential” war with Saudi-backed Yemeni government forces, characterising the conflict as a fight against radical Islamism – a longtime preoccupation of the UAE.

Saudi Arabia and the UAE have for years supported rival factions in Yemen’s government-run territories, but the STC’s offensive has angered Riyadh and left the oil-rich Gulf powers at loggerheads.

Mohammed Abdulmalik, head of the STC in Wadi Hadramaut and Hadramaut Desert, said seven airstrikes hit the al-Khasah camp, killing seven and wounding more than 20.

Further strikes targeted other sites in the same region, he added.

The air raids came shortly after pro-Saudi forces launched a campaign to “peacefully” take control of military sites in Hadramawt.

“This operation is not a declaration of war, nor an attempt to escalate tensions,” Hadramawt governor, Salem al-Khanbashi, also leader of the province’s Saudi-backed local forces, was quoted as saying by the Saba Net news agency.

“This operation does not target any political or social group,” he said, adding that it “aims to peacefully and systematically hand over military sites”.

Saudi sources confirmed the strikes were carried out by the Saudi-led coalition, which also nominally includes the UAE and was formed in 2015 to fight the Iran-backed Houthi rebels in Yemen’s north.

A source close to the Saudi military warned: “It will not stop until the Southern Transitional Council withdraws from the two governorates.”

The STC seized much of Hadramawt, bordering Saudi Arabia, and neighbouring Mahra last month.

The wealthy Gulf powers formed the backbone of the military coalition aimed at dislodging the Houthis, who forced the government from the capital Sana’a in 2014 and seized Yemen’s most populated areas.

But after a brutal, decade-long civil war, the Houthis remain in place and the Saudis and Emiratis are backing different factions in the government-held territories.

Amr Al Bidh, foreign affairs representative for the STC, accused Riyadh of having “knowingly misled the international community by announcing a ‘peaceful operation’ that they never had any intention to keep peaceful”.

“This was evidenced by the fact that they launched 7 airstrikes minutes later,” he posted on X.

Saudi Arabia has repeatedly urged the STC to withdraw from the recently conquered territories.

After the Saudi-led coalition bombed an alleged Emirati weapons shipment on Tuesday, the UAE’s defence ministry said it would withdraw its remaining troops in Yemen.

The Yemeni government comprises a fractious coalition of groups, including the STC, united by their opposition to the Houthis.

The STC’s advance has raised the possibility that South Yemen, a separate state from 1967 to 1990, might declare independence, while dealing a hammer blow to slow-moving peace negotiations with the Houthis.

Also on Friday, the Saudi ambassador to Yemen, Mohammed al-Jabir, said the STC had blocked a Saudi delegation from landing at Aden airport, accusing the group of “intransigence”.

On Thursday, Yemen’s STC-controlled transport ministry denounced a Saudi demand that all planes to and from the UAE make a stop in Saudi Arabia for security checks.

According to the Flightradar24 tracking website, no planes have taken off or landed at Aden airport for more than 24 hours, although the ministry did not officially announce its closure.