The UN special envoy for Yemen, Martin Griffiths, has expressed concern about a military escalation in Yemen's southern port city of Aden, the seat of its internationally recognized government.

Southern separatists clashed there on Wednesday with presidential guards; one person was killed and at least two were badly injured, Reuters reported, citing local officials and residents. Just before Wednesday’s clash, hundreds of separatist supporters had attended a funeral for some southern soldiers and a prominent commander, which took place near the presidential palace.

The separatists and the internationally recognized government of President Abd-Rabbu Mansour Hadi are nominally united in their battle against the Houthis.

The UAE's Minister of State for Foreign Affairs Anwar Gargash called for calm after the violence, which he described as worrying. Gargash said escalation between the two sides was not acceptable, after attacks claimed by Islamic State (IS, formerly ISIS) and Al-Qaeda in southern Yemen in recent days.