Yemen's presidency on Monday condemned recent developments in southern Aden province, describing them as "tantamount to a coup".
According to Yemen's official SABA news agency, President Abdrabbuh Mansur Hadi convened an emergency meeting to discuss what he described as "an illegitimate coup attempt by the so-called Southern Transitional Council (STC)".
Hadi went on to describe the council as "southern separatists".
SABA quoted one meeting participant, who the news agency did not name, as saying: "What is happening in Aden is an illegitimate coup d'état characterized by irresponsible acts that have terrified local residents who support the country's legitimate government."
"These acts," the source said, "raise a number of questions as to who benefits, especially given recent military successes -- on multiple fronts -- against Houthi rebels."
According to recent reports by Yemen's Health Ministry, at least 16 people have been killed in Aden and scores more injured in recent clashes between pro-government forces and southern separatists.
Early Tuesday, the International Committee of the Red Cross said in a statement that 36 people had been killed and 180 wounded in clashes since Sunday.
Violence reportedly erupted on Sunday after forces loyal to the STC seized the government's headquarters in the coastal city.
Tension has steadily mounted in Aden since the STC called for the dismissal of Prime Minister Ahmed bin Daghr, accusing his government of pushing war-torn Yemen to the brink of starvation.
The U.S. voiced concern over the clashes, urging all sides to refrain from violence and address grievances in dialogue.
"A political dialogue represents the only way to achieve a more stable, unified and prosperous Yemen," State Department spokeswoman Heather Nauert said in a statement. "The Yemeni people are already facing a dire humanitarian crisis. Additional divisions and violence within Yemen will only increase their suffering."
In 2014, Houthi rebels overran much of the country, including the capital Sanaa, forcing Yemen's Saudi-backed government to set up an interim capital in Aden.
In 2015, Saudi Arabia and its Sunni-Arab allies -- who accuse the Houthis of serving as an Iranian proxy -- launched a massive military campaign aimed at rolling back Houthi gains.
