A U.S. drone strike targeted suspected militants of the Yemen-based al-Qaida offshoot at a checkpoint in Yemen's southeastern province of Shabwa on Thursday, leaving four killed, a security official told Xinhua.

"About four al-Qaida militants were killed and three others injured when their own tent and a checkpoint were targeted by U.S. missiles in Azzan town of Shabwa province," the Yemeni security source said on condition of anonymity.

Residents confirmed to Xinhua that U.S. drones kept hovering over the airspace of Azzan for several hours and huge blasts were heard in the area.

Elsewhere in Yemen's southern part, suspected al-Qaida militants hurled grenades on two police stations in the port city of Aden, causing only material damages.

According to government officials, large Yemeni-Saudi military preparations continued in Aden on Thursday to launch a new anti-terror offensive to flush out al-Qaida militants from Abyan in the upcoming days.

Last December, gunmen of the al-Qaida in the Arabian Peninsula (AQAP) took full control over two strategic towns in Abyan, about 45 km from Aden, where Yemen's internationally recognized government is based.

Yemen, an impoverished Arab country, has been gripped by one of the most active regional al-Qaida insurgencies in the Middle East.

The AQAP, also known locally as Ansar al-Sharia, emerged in January 2009. It had claimed responsibility for a number of terrorist attacks on Yemen's army and government institutions.

It took advantage of the current security vacuum and the ongoing civil war to expand its influence and seize more territories in Yemen's southern part.

Security in Yemen has deteriorated since March 2015, when war broke out between the Shiite Houthi group, supported by former President Ali Abdullash Saleh, and the government backed by a Saudi-led Arab coalition.

More than 6,400 people have been killed in ground battles and airstrikes since then, half of them civilians.

Source : XINHUA