Pro-government forces in Yemen have launched an offensive on the rebel-held capital of southern Abyan province, military sources say.
They say the troops, using tanks and other military equipment supplied by a Saudi-led coalition, were attacking Zinjibar from the north and south.
The fall of the city would deal another blow to the Houthi rebels, who have suffered a number of recent defeats.
They were driven out of a key airbase this week, following the loss of Aden.
Heavy casualties were reported during the fighting for al-Anad airbase, north of Aden.
Separately, the United Arab Emirates’ official WAM agency said on Saturday that three Emirati soldiers were killed while taking part in the Saudi-led campaign to defeat the rebels who still control much of Yemen, including the capital Sanaa.
The Houthis advanced south in March, forcing President Abdrabbo Mansour Hadi to flee to Saudi Arabia.
Why is there fighting in Yemen?
- Northern Shia Muslim rebels known as Houthis, backed by forces loyal to Yemen’s ex-president, took over parts of Yemen, including Sanaa, and forced the government into exile in March
- The rebels accused the government of corruption and of planning to marginalise their heartland within a proposed federal system
- Forces loyal to the government, and southern militia, are fighting back, aided by air strikes led by neighbouring Saudi Arabia
Yemen crisis: Who is fighting whom?
Sunni power Saudi Arabia regards the Houthis as proxies of Shia rival Iran. It alleges Iran has provided the Houthis with weapons, something Iran and the Houthis deny.
The rebels – backed by forces loyal to former President Ali Abdullah Saleh – say they are fighting against corruption and marginalisation of their northern powerbase by Mr Hadi’s government.
The conflict has killed almost 4,000 people, nearly half of them civilians, since it escalated with the Saudi-led campaign in March, according to the United Nations.