Story highlights An unmanned aircraft carried out the strike, says a U.S. official

Another U.S. official says the results of the operation are being assessed

Al-Shabaab is an Islamist militant group, linked to al Qaeda

(CNN) The United States conducted an airstrike Monday in Somalia against Al-Shabaab, said Navy Rear Adm. John Kirby, Pentagon press secretary.

The strike, which took place in the area of Saakow, was targeting a senior leader of the Islamist militant group.

"At this time, we do not assess there to be any civilian or bystander casualties. We are assessing the results of the operation and will provide additional information, when appropriate, as details become available," Kirby said in a statement.

The strike was carried out by an unmanned aircraft, and was an operation of the U.S. Defense Department, according to a U.S. defense official, who spoke on the condition of anonymity.

On Saturday, Somalia government forces captured a top Al-Shabaab commander, said two of the country's military officials.

Read More