Yemen army kills 13 Islamists in south ADEN (Reuters) - At least 13 Islamist fighters linked to al Qaeda were killed in clashes with Yemen's army in the impoverished country's south on Thursday, the government and militants said. Yemen has launched an offensive against Islamist insurgents in the territory who have taken advantage of the chaos surrounding more than a year of mass protests and fighting that unseated former president Ali Abdullah Saleh. At least seven militants were killed near the southern Yemeni city of Lawdar on Thursday, the defense ministry's news service reported in a text message. Four of the members of the Ansar al-Sharia (Partisans of Islamic Law) group were Somalis, it added. Six militants were also killed in clashes with the Yemeni army in the southern city of Zinjibar, a spokesman for Ansar al-Sharia told Reuters. An army official said two soldiers were killed and four others wounded in the clashes. Islamist insurgents have already taken control of a number of cities in the southern territory which is close to key shipping lanes in the Red Sea. The interior ministry said it had received unconfirmed reports of a plot by al Qaeda suicide bombers to attack gas facilities in Belhaf in the southern Shabwa province and security forces were on the alert. Yemen's oil and gas pipelines have been repeatedly sabotaged since last year's anti-government protests created a power vacuum in parts of the country. Yemen's government has regularly reported al Qaeda plots to launch further attacks, but it has not been possible to confirm the reports independently. France's Total gas pipeline to Balhaf was last blown up in March, hours after a U.S. drone attack killed at least five militants. The ministry added Yemen had tightened security around the Saudi embassy in Sanaa after an al Qaeda-linked militant claimed responsibility for last month's kidnapping of a senior Saudi diplomat. Yemen's new president, Abd-Rabbu Mansour Hadi, who took office vowing to fight al Qaeda, is also facing challenges from Shi'ite Muslim rebels in the north and secessionists in the south. Reporting by Mohammed Mukhashaf in Aden and Mohammed Ghobari in Sanaa; Writing by Mahmoud Habboush and Rania El Gamal; Editing by Andrew Heavens