A soldier and an aid worker from the United Arab Emirates have been killed in Yemen where their country is taking part in a Saudi-led military campaign against Iranian-allied Houthi militiamen, Emirati and Yemeni sources said on Saturday.

The UAE's state news agency WAM identified the soldier as Captain Hadef Hameed al-Shamesi but gave no details about his death.

Separately, a Yemeni security officer said an Emirati aid worker had been shot dead by unknown gunmen on Saturday in Aden, in a sign of continued instability in the southern port city where Yemen's fragile government is based.

The Yemeni source said the Emirati had been travelling in an armoured Land Cruiser with a group of his compatriots when he was killed.

"He was shot dead when he exited the vehicle near a store by gunmen pursuing in another car," said the official.

It was not immediately clear whether there was any link between the killings of the aid worker and the soldier.

No one has claimed responsibility for the deaths, but al Qaeda and Islamic State have both gained ground in Yemen, where a war has been raging for seven months between the Saudi-led military alliance and the Houthi militiamen.

In a series of suicide bombings on Oct. 6 in Aden and the capital Sanaa, Yemen's branch of Islamic State killed a total of 22 people, including several troops from the United Arab Emirates, at the government headquarters in Aden and other coalition outposts in the city.

It was the biggest attack on the government and its coalition ally since Gulf Arab and Yemeni troops retook the city from its Houthi forces in July.

Ground fighting and Saudi-led air strikes have killed at least 5,400 people in Yemen's multi-sided conflict, which started as a civil war among competing factions but has drawn in outside powers in a regional struggle for influence between Sunni Muslim Gulf countries and Shi'ite Iran.

The Yemeni government returned from exile in Saudi Arabia last month and set up its temporary headquarters in Aden's al-Qasr hotel.