ADEN (Reuters) - Southern Yemeni separatists clashed with government forces in the southern oil-producing province of Shabwa on Thursday, local officials and residents said, in the latest violence between nominal allies that has strained an Arab military coalition.

The United Arab Emirates-backed separatists earlier this month took over Aden port, interim seat of Yemen’s Saudi-backed government, and last week they extended their control to neighboring Abyan.

Both sides are part of a Saudi-led coalition that intervened in Yemen in 2015 against the Iran-aligned Houthi group that ousted the government of President Abd-Rabbu Mansour Hadi from power in the capital Sanaa in late 2014.

But the separatists, the Southern Transitional Council (STC), who seek self-rule in the south, turned on the government after accusing a party allied to Hadi of being complicit in a Houthi attack on southern forces.

Saudi Arabia has called for a summit to end the standoff, which has complicated U.N. efforts to end the war in Yemen. But Hadi’s government said it would not participate until the separatists cede control of sites they have seized.

The standoff has exposed differences between regional allies Saudi Arabia and the UAE, which in June scaled down its presence in Yemen while still backing thousands of southern separatist fighters.