Gunmen attacked offices for humanitarian aid groups in Yemen's southern province of Dhalea early on Sunday, a security official said.

The unknown gunmen fired a number of rocket-propelled grenades against five offices of international humanitarian aid groups in Dhalea city, causing no casualties, the security source said on condition of anonymity.

He said that the coordinated armed attacks forced the international non-government organizations to shut down and evacuate all the employees to Aden province.

No armed group has yet claimed responsibility for the attacks.

Yemen has been plagued in a civil war for more than four years which has killed tens of thousands of people, displaced three million and pushed the country to the brink of famine.

The Yemeni government, allied with the Saudi-led Arab military coalition, has been battling Iran-backed Houthis for the control of the country since 2015.