SANAA, Aug. 7 (Xinhua) -- The United Nations Special Envoy to Yemen Martin Griffiths on Wednesday expressed deep concerns over a military escalation in the southern port city of Aden, the temporary capital of Yemen's internationally-recognized government.

"I am alarmed by the military escalations in Aden, including reports of clashes in the vicinity of the presidential palace. I am also deeply concerned by the recent rhetoric encouraging violence against Yemeni institutions," he said in a statement.

"Escalations of violence will contribute to instability and suffering in Aden and will deepen Yemen's political and social divisions," he said.

"I call on the parties involved to abandon violence and engage in dialogue to resolve differences."

At least two people were killed and dozens injured earlier in the day in clashes between southern separatists and the presidential guards in Aden, according to medics and residents.