UPDATE 4-Somali Shabaab rebels say they shot down U.S. drone

* Drone was flying over southern port of Kismayu

* Insurgents hunt for wreckage

* Shabaab targets Sufi holy sites in central region

(Adds U.S. Navy comment in paragraph 5) By Abdi Sheikh

MOGADISHU, Oct 19 (Reuters) - Insurgents of the Somali al Shabaab group shot down a U.S. drone aircraft flying over the southern port of Kismayu on Monday and were searching for the wreckage, an insurgent spokesman said.

U.S. commandos killed a 'most wanted' al Qaeda suspect allied to al Shabaab last month in a helicopter raid in the rebel-held south of the failed state.

"We fired at an American plane spying for information over Kismayu. Our forces targeted the plane and shot it and we saw the plane burning. We think it fell into the sea," said Sheikh Hassan Yacqub, spokesman for al Shabaab in Kismayu.

"We are still searching for it," he told Reuters.

Lieutenant Nathan Christensen, spokesman of the U.S. Navy's Fifth Fleet in Bahrain, said all its unmanned aerial vehicles had been safely recovered but could not give further details.