At least 12 people have been killed and more than 130 wounded in Yemen's coastal city of Aden in clashes between government forces, backed by Saudi Arabia, and southern separatists backed by the United Arab Emirates (UAE).
The Yemeni Health Ministry said at least four people were killed on Monday and eight on Sunday after the military wing of the Southern Transitional Council (STC), a political movement demanding secession for southern Yemen, seized control of government headquarters.
Residents told Al Jazeera that in Aden's districts of Khormaksar and Dar Saad, the two sides exchanged heavy gunfire throughout the day, as the streets lay empty of traffic and shops and schools remained closed.
One eyewitness reported a "fierce" street battle between fighters loyal to the STC and Yemeni forces, causing panic among civilians.
Meanwhile, the international aid organisation Oxfam said the violence had forced it to close its offices.
Tension has been running high in Aden since the STC gave President Abd-Rabbu Mansour Hadi's government an ultimatum last week, to either dismiss Prime Minister Ahmed bin Daghr and his cabinet, or face an overthrow.
Hadi's government refused to be coerced and subsequently banned public gatherings ahead of Sunday's deadline.
'Rebellion won't achieve peace'
Speaking from the Saudi capital Riyadh, where he was forced into exile two years ago, Hadi renewed his call for a ceasefire, urging the separatists to end their "coup."
"Rebellions and weapons won't achieve peace or build a state," he said on Monday.
"The real and the main battle is with the Houthis and any other side problems will impact the main battle. Any assault on legitimacy is a coup."
Mohammed Ali al-Miqdashi, a senior military adviser to the president, said the STC's rebellion could render them an "enemy".
"There is no difference between the Houthis and anyone else who rebels against the legitimate government, no matter who they are.
"If he is not with the legitimate government then he is rebelling against it and considered an enemy to the entire country," he said.
The latest developments in Aden underscore the rising tensions between Hadi's government and the UAE.
The UAE entered Yemen's war in March 2015 as part of a Saudi-led coalition seeking to roll back advances made by Houthi rebels after they overran much of the country, including the capital Sanaa, in 2014.
Nearly three years on, the coalition has failed to achieve its stated aim of restoring the "legitimate" government of Hadi.
Saudi Arabia has said it "wants out" of the costly exercise, but the UAE has become more involved in the conflict, indicating a divide in the two countries' agendas.
The UAE has financed and trained armed groups in the south who answer to it, and set up prisons and created a security establishment parallel to Hadi's government, according to Human Rights Watch.