Al-Qaeda in Yemen previously focused on high-impact strikes against Western and Saudi targets, but appears now to be targeting government forces in response to enhanced Yemen-US security coordination and a government crackdown.

"There was an ambush targeting the soldiers' vehicle and five were killed and a sixth was wounded. There is suspicion that Al-Qaeda was behind the operation," an official in the southern province of Shabwa told Reuters.

Yemen, next door to top oil exporter Saudi Arabia, leapt to the forefront of Western security concerns after Al-Qaeda's Yemen-based regional wing claimed responsibility for a failed attempt to bomb a US-bound plane in December.

Mustafa Alani, an analyst at the Gulf Research Center, expected attacks on both Western targets in Yemen and local security forces to continue. "It is basically reflecting their renewed strategy that they are going to fight the government, which has allied itself with the Saudis and the Americans," he said.

Yemen's often poorly guarded security forces are easier to strike than many Western targets, and the group may hope to capitalize on anti-government sentiment in the south, home to a strong separatist movement.

Last month, gunmen raided the regional headquarters of the political security office in Aden, killing 11, an attack Al-Qaeda said was revenge for a state assault on a militant stronghold.

Last week, more suspected Al-Qaeda gunmen attacked two security buildings, igniting clashes that killed four people.

Violence also flared in north Yemen, where a machine-gun-and-mortar battle pitted Shiite rebels against pro-government tribesmen and security forces, killing 19 people and threatening a truce to end an intermittent northern civil war.

The fighting was the bloodiest in the north since a truce was sealed in February to end the war, which has raged on and off since 2004 and displaced 350,000 people. Analysts say the truce may not last unless Sanaa better addresses grievances.

"There were very violent confrontations. Nine soldiers and pro-government tribesmen were killed as well as about 10 Houthis (rebels)," a local official in the Harf Sufyan region said.

"It remains very tense after the failure of efforts to stop the fighting between the two sides," he added.

Yemen's allies want Sanaa, also trying to quell southern separatism, to resolve domestic conflicts like the war in the north so it can focus on fighting Al-Qaeda. But tensions between the rebels and tribes in the country's north have been rising in the Harf Sufyan area for months, and exploded after rebels attacked a tribal leader's home in early July, killing three of his followers.