WASHINGTON β€” The U.S. military said the situation at a Kenyan airfield used by U.S. forces was "fluid" after a pre-dawn attack by the al-Shabab extremist group.

Capt. Gilbert M. Kibe, the Director General for Kenya's Civil Aviation Authority said in a statement that the agency has reopened the Lamu Civilian Airstrip operated by the Kenya Airports Authority after it was temporarily closed because of an "early morning incident in Lamu County."

A different statement said the Manda Bay airfield was "still in the process of being fully secured." The initial statement didn't mention any casualties. 

The Associated Press reported that a U.S. Africa Command statement read,  β€œan accountability of personnel assessment is underway.” Irungu Macharia, the commissioner of Lamu county said that there were five suspects arrested, and they were being interrogated. 

The Somalia-based al-Shabab claimed that intense combat continued, and it said the attack had nothing to do with the Middle East crisis. This is the first known al-Shabab attack against U.S. forces inside Kenya, a key base for fighting one of the world's most resilient extremist organizations.

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Reports said that a plume of black smoke could be seen above the base and people in the area said a car bomb exploded earlier that morning. 

As Reuters reports, al Shabaab has continued a mission of deadly attacks even after being pushed out of their bases in Somalia's capital of Mogadishu, along with other areas in the region over the years. 

Camp Simba is the military's camp in Lamu County and it was established over ten years ago. The camp has 100 U.S. personnel according to the Pentagon. U.S. forces at Manda Bay airfield train East African partners and give counter-terror support.