The Somali government says al-Shabab fighters have attacked troops in northern Mogadishu, continuing a string of attacks in the capital after a period of relative calm.

Officials say the al-Qaida-linked group mounted an offensive on government positions Thursday in the northern Huriwa and Karan districts.

Both sides claimed to have caused enemy casualties, although their reports could not be independently confirmed.

Al-Shabab withdrew its fighters from the capital in August after the government launched an offensive with the support of African Union troops. The Islamist group said the move was “tactical” and vowed to return.

Since late November, there have been 15 bomb attacks in Mogadishu, and the government has blamed them on al-Shabab.

In an interview with VOA on Thursday, a former official with Somalia's National Security Agency said al-Shabab appears to have adopted guerilla tactics to destabilize Mogadishu.

Colonel Abdulahi Ali Maow also said al-Shabab appears to have created a unit of more sophisticated fighters, some of whom may have infiltrated pro-government forces.

Elsewhere in southern Somalia on Thursday, witnesses say unidentified fighter jets bombed al-Shabab bases, killing at least one person.

The planes fired missiles on the town of Bardhere, located on the Juba River about 350 kilometers west of Mogadishu.

It was not clear who was behind the air attacks, but Kenyan military forces have carried out airstrikes in the region in recent months.

Kenya's military moved into southern Somalia in October to pursue the al-Qaida-linked group, after accusing its fighters of kidnapping foreigners on Kenyan soil.

The militants say they are fighting to overthrow Somalia's United Nations-backed government and impose a strict form of Islamic law.