Somalia's al-Shabaab extremists on Sunday attacked a military base in Lamu county in Kenya that is used by both U.S. and Kenyan forces, a government official said.

"There was an attack but they have been repulsed," Lamu Commissioner Irungu Macharia said.

A military source said the fighters were trying to access the base from the airstrip.

Witnesses said gunfire and blasts were heard.