ADEN (Reuters) - At least 25 suspected al Qaeda-linked militants were killed on Wednesday in a third day of fighting with Yemeni troops in the south of the country, residents and local officials said. Officials said the clashes took place at Jebel Yasuf, some 10 km (6 miles) from the town of Lawdar, where dozens of people have been killed since Monday, when fighters from Ansar al-Sharia (Partisans of Islamic Law) group attacked a military camp there. Militants emboldened by a year of political upheaval in Yemen are trying to exploit weakened security forces to extend their control over the country's south, particularly Abyan province, where they already hold large swathes of territory. Lawdar is located in Abyan. The Defense Ministry said in a text message it had destroyed a number of checkpoints set up by militants on a main road linking Lawdar to the neighboring province of al-Bayda, re-opening the route. It also cited unnamed military sources as saying that Saudi Arabian, Pakistani and Somali nationals were among the militants killed in the Lawdar area. President Abd-Rabbu Mansour Hadi vowed to fight al Qaeda and its affiliates when he took office earlier this year after his predecessor quit under pressure from anti-government protesters and foreign powers anxious to halt a slide into mayhem. Militants have since stepped up their operations against the army, carrying out a string of deadly attacks that have cast a long shadow over the country's first months post-Ali Abdullah Saleh. In return, the Yemeni air force has launched air strikes on suspected militant strongholds and the United States has joined in with drones. The United States and Saudi Arabia - both targets of al Qaeda's Yemen-based wing - fear Yemen is becoming a major front in its campaign against the militant network, which has been dealt a number of blows over the past year, not least the killing of its founder and leader Osama bin Laden. Reporting by Mohammed Mukhashaf; Writing by Isabel Coles; editing by Sami Aboudi/Maria Golovnina