An army tank shelled a funeral tent erected by the Southern Movement at a school in Yemen on Friday, killing 13 people including children, a medic and witnesses said.

Tensions are running high in the formerly independent south, home to an increasingly assertive secessionist movement, raising fears that Al-Qaeda's powerful Yemen affiliate could exploit the growing unrest in the Arab world's poorest country.

A long-running dispute over whether and how to grant the south limited autonomy has hindered the political transition following the 33-year rule of Ali Abdullah Saleh, who stepped down last year following Arab Spring-inspired protests.

"Thirteen people have died, among them three children" in the attack, a medic from Al-Nasr hospital in the southern province of Daleh told AFP. Medics at other hospitals said more than 20 people were wounded, some critically.

Witnesses said a tank shelled the tent in Sanah, 300 kilometres (185 miles) south of the capital, with one telling AFP that troops had kept firing "when we tried to hospitalise the casualties", adding that "there are wounded victims still inside the tent".

Witnesses later the wounded were finally evacuated.

The Southern Movement -- which is campaigning for autonomy or outright secession -- had set up the tent for mourners paying their condolences after a man was killed in clashes with security forces on Monday.

The clashes in Daleh erupted when secessionists tried to storm the governorate building to hoist the flag of the former South Yemen. The fighting left two Yemeni policemen and a civilian dead.

State news agency Saba quoted a top security official as saying that President Abdrabuh Mansur Hadi has formed a committee to investigate Friday's attack.

Violence has intensified in the south amid anger over the killing of local tribal chief Said Ben Habrish and his bodyguards at an army checkpoint earlier this month after they refused to hand over their weapons. Two soldiers were also killed in the exchange.

On Thursday, gunmen killed four soldiers and wounded several others in an attack on a checkpoint in the southeast Hadramawt province, an Al-Qaeda stronghold.

Hardline southern faction

A security official told AFP a cousin of South Yemen's exiled vice-president Ali Salem al-Baid was among the militants who assaulted the checkpoint, accusing the Southern Movement and the Hadramawt tribal alliance of being behind the attack.

Baid leads a hardline faction of the Southern Movement that, alongside the tribal alliance, has protested over Ben Habrish's death.

But a leader of the tribal alliance denied any involvement in the checkpoint attack.

The violence has sparked warnings by Yemeni officials that Al-Qaeda in the Arabian Peninsula, blamed for most of the increasingly common hit-and-run strikes on military personnel and officials, could exploit the growing unrest in the south.

"Yemeni armed forces have two enemies fighting them -- Al-Qaeda and the tribal alliance. We no longer know which of them is behind attacks targeting checkpoints and military camps," a military official told AFP.

Deputy Interior Minister Naser Lakhsha expressed similar fears, saying "several army camps and checkpoints have come under attack in recent days" in the south.

Protest organisers are pressing authorities to hand over the suspect accused of killing Ben Habrish and to provide jobs for southerners in the security forces and oil sector.

Lakhsha told AFP the government could respond to the "legitimate demands" of the people in Hadramawt.

After British colonial rule ended in 1967, southern Yemen was independent until union with the north in 1990.

A secession attempt four years later sparked a brief but bloody civil war that ended with northern forces taking over the south.

Also in Hadramawt on Friday, an alleged US drone strike killed two Al-Qaeda suspects, an official said.

"The drone raid targeted a vehicle in which two Al-Qaeda suspects were travelling, completely destroying it and killing them," the official in Hadramawt told AFP.

The identity of the suspects was not immediately known.