CAIRO (AP) — The Saudi-led coalition in Yemen warned Saturday it would immediately respond to any military movements of separatists backed by the United Arab Emirates that undermine de-escalation efforts in the southern region of Yemen, as the United States urged diplomacy.

“Any military movements that violate these efforts will be dealt with directly and immediately in order to protect civilian lives and ensure the success of restoring calm," said Brig. Gen. Turki al-Maliki, a coalition spokesman, according to the Saudi Press Agency.

Al-Maliki also accused the Southern Transitional Council, or STC, separatists of “serious and horrific human rights violations against civilians,” without providing evidence.

This came a day after separatists accused Saudi Arabia of targeting their forces with airstrikes, something not formally acknowledged by the kingdom, whose relations with the UAE have been strained because of STC actions.

U.S. Secretary of State Marco Rubio said in a statement Saturday that his country was “concerned by recent events in southeastern Yemen” and urged restraint and diplomacy to reach “a lasting solution.” He also expressed gratitude “for the diplomatic leadership of our partners, the Kingdom of Saudi Arabia and the United Arab Emirates.”

Yemen, engulfed in a civil war for more than a decade, has the Iran-aided Houthis controlling much of the northern regions, while a Saudi-UAE-backed coalition supports the internationally recognized government in the south. However, the UAE also helps the southern separatists who call for South Yemen to secede once again from Yemen.

The council moved earlier this month into Yemen’s governorates of Hadramout and Mahra and seized an oil-rich region. That had pushed out forces affiliated with the Saudi-supported National Shield Forces, another group aligned with the coalition in fighting the Houthis.

The coalition now demands the withdrawal of STC forces from the two governorates, with local authorities returning to oversee them, and the handover of their military camps.

Rashad al-Alimi, head of Yemen’s Presidential Leadership Council, the governing body of the internationally recognized government, said after an emergency meeting late Friday that STC movements posed “serious violations against civilians.”

The coalition said in its Saturday announcement came at al-Alimi's request to protect civilians in Hadramout.

The U.N. Office of the Special Envoy of the Secretary-General for Yemen said Saturday that it's closely following developments in Hadramout and Mahra, reiterating calls for restraint, de-escalation, dialogues and for all parties to avoid further escalation.