Pressure builds on key Yemen city
Fighting in the Yemeni city of Aden has intensified as Houthi rebels try to seize control of the city.
Concern is growing over the number of casualties after heavy clashes between local militia fighters and rebel forces.
Witnesses have reported bodies lying in the street after rebel shelling and sniper attacks.
The fierce fighting has continued despite airstrikes on Houthi forces by a Saudi-led coalition.
Houthi rebels allied with troops loyal to the former President Ali Abdullah Saleh have reportedly advanced deeper into Aden to try and wrest control of the city from fighters loyal to President Abdrabbuh Mansour Hadi.
The BBC's Security Correspondent Frank Gardner says that if reports of rebel tanks entering the centre of the southern port city are confirmed, then the rebels will have consolidated their grip on the most important parts of Yemen.
As the fighting continues, there have been increasing concern about the number of casualties.
A spokeswoman for the aid agency Medecins Sans Frontieres (MSF) told the BBC that its hospital in Aden had received more than 500 injured people from all sides in the conflict over the last two weeks.
"The major injuries are gunshots and since the bombs we have some people with injuries linked to explosions," said spokeswoman Marie-Elisabeth Ingres.
On Wednesday, AFP news agency reported that at least 19 people had been killed, including six civilians, in clashes in the city's Khor Maksar district.
The UN has also expressed alarm at the rising number of civilian deaths in Yemen.
On Tuesday, the high commissioner for human rights warned that the country seemed to be "on the verge of total collapse".
President Hadi fled abroad last week after rebels advanced on Aden, where he had taken refuge after the Houthis took full control of the capital Sanaa in January and placed him under house arrest.
A Saudi-led coalition is attempting to help Hadi in his fight against the Houthis by conducting airstrikes against the rebels and their allies.
On Wednesday, at least 35 workers were killed by a blast at a dairy factory in the Red Sea port city of Hudaydah.
There were conflicting reports about the cause of the overnight explosion but witnesses said coalition aircraft hit warehouses belonging to the factory.
The latest violence comes as dozens of Yemenis are reported to have crossed the Gulf of Aden in small boats to get to Somalia and Djibouti to escape fighting and airstrikes on the city of Taez.
The arrival of the Yemeni refugees reverses a decades-old trend in which thousands of Somalis have sought sanctuary in Yemen to escape their own country's violence.
The Houthis have said their aim is to replace President Hadi's government, which they accuse of being corrupt. Their leader has refused to surrender to what he called the "unjustified aggression" by the coalition.