Two pilots died when a UAE Mirage plane crashed in Yemen on Monday due to a technical fault while conducting military operations for the Saudi-led alliance, the coalition said in a statement carried by Saudi state media.

Local Yemeni officials said the plane was flying low when it crashed into a mountain after it conducted bombing raids in Buraiqa district in northwestern Aden where Islamist militants are based.

Hani Al-Yazidi, director of the Buraiqa district in Aden, said authorities had found the plane's wreckage after it had crashed into a mountain.

Another local official, who declined to be identified, said rescue teams had found the body of one of the pilots and were searching for the second.

Pictures taken by a Reuters photographer showed local fighters holding pieces of wreckage believed to be part of the plane. Another photograph showed rescue personnel loading what appeared to be the body of one of the pilots into a truck.

The UAE armed forces had earlier said in a brief statement that the jet taking part in the fighting was "lost".

The government of President Abd-Rabbu Mansour Hadi, backed by the Saudi-led coalition, has embarked on a campaign against Islamist militants based in northern Aden whom it accuses of being behind armed attacks and suicide bombings that have killed scores of people since last year.

Helicopters from the Saudi-led coalition have taken part in the military operations which were concentrated in Al-Mansoura district, east of Buraiqa, where at least 18 people had died in overnight fighting on Sunday.

Residents reported more helicopter overnight strikes on Monday that lasted until the morning. Yemeni forces later entered a block where the militants had been holed up without resistance and seized the local council building which had been controlled by the fighters.

The militants had apparently fled before the troops went in.

The coalition entered Yemen's civil war in March last year to try to restore President Abd-Rabbu Mansour Hadi after Iran-allied Houthis and forces loyal to former president Ali Abdullah Saleh ousted him from power.

There was no immediate comment from the Saudi-led coalition.

At least two jets from the alliance have crashed since the start of the campaign.

In May 2015 a Moroccan F-16 warplane crashed while on a mission with the alliance in Yemen, and the Houthi militia said tribesmen had shot down the aircraft.

In December a Bahraini F-16 jet from the coalition crashed in Yemen's neighbour, Saudi Arabia, after a technical fault.  - Reuters