Yemeni authorities say fighting between Yemeni troops and al-Qaida-linked militants in the country's south killed at least 18 people Wednesday and Thursday.

Western news agencies quote Yemeni security officials, medics and a source close to the insurgents as saying the dead include at least 15 militants and three government soldiers. They say the battles happened around the city of Zinjibar, which the militants seized in May, taking advantage of political chaos in the country.

Yemeni officials repeatedly have said government troops are closing in on militant strongholds in Abyan province, whose capital is Zinjibar. But, the Yemeni military has faced strong resistance from the militants in months of fighting. The officials said Thursday Yemeni forces have broken a militant siege around a military unit on the outskirts of Zinjibar. There was no independent confirmation of the claim.

Yemen has been plagued by political unrest since February, when opposition activists began staging frequent mass protests to demand an immediate end to the autocratic rule of longtime President Ali Abdullah Saleh. The president has been in Saudi Arabia since being severely wounded in a June 3 bomb attack on his Sana'a compound. He has vowed to lead a process of political reform and hold a new presidential election.

It is not clear when or if he will return to Yemen.