Eight people, including a military commander, were killed as an army helicopter was shot down by tribesmen over an al-Qaida stronghold in Yemen.
The helicopter was downed as the US and UK governments have withdrawn diplomatic staff from the country over security threats.
Yemeni officials said the helicopter was hit by a rocket as it was flying over Wadi Ubida, in the lawless province of Marib.
The aircraft was part of a military force guarding oil installations in the province.
An eyewitness told Reuters that it had engaged in gunfight with a group of local tribesmen accused of blowing up a pipeline linking eastern oilfields to the Red Sea coast last week.
"The helicopter was firing from a low altitude at armed tribesmen," the witness said.
An interior ministry official speaking on condition of anonymity confirmed the account to Chinese news agency Xinhua.
"The chopper was flying low while it was attacked by heavy gunfire that caused it to crash into the ground," the official said.
"The commander of 107th Brigade, Hussein al-Mashaba, as well as two pilots and five crew members were killed in the crash."
Al-Mashaba was the head of Yemen's force tasked with protecting oil installations.
Yemen is one of the most impoverished Middle East countries and its state budged largely depends on oil revenues.
Pipe lines are however often targeted by armed tribesmen challenging state authority, in an area that is home also to al-Qaida local branch, al-Qaida in the Arabian Peninsula (AQAP).
Intercepted conversations between top al-Qaida leader Ayman al-Zawahiri and AQAP chief Nasser al-Wahishi have prompted the closure of 20 US embassies and consulates in North Africa and the Middle East.