(Reuters) - U.S. forces targeted a leader of the al Shabaab militant group in an operation in southern Somalia this week, the Pentagon said on Friday, a day after villagers reported a drone strike killed three members of the al Qaeda-affiliated organization.

U.S. officials declined to name the target of the strike, but CBS News and other U.S. and African media said it was aimed at Adnan Garaar, a top al Shabaab official suspected of masterminding the 2013 attack on Westgate shopping mall in Nairobi, killing 67.

The wide reporting of Garaar as the target prompted the U.S. Embassy in Nairobi to caution U.S. citizens to be aware of their safety given the news accounts of the drone strike.

CBS cited unnamed U.S. officials as confirming Garaar was killed in the strike, which it said was carried out by a Predator drone using Hellfire missiles. U.S. defense officials speaking on the record declined to identify the target of the operation or give details, including whether he had been killed.

"We are currently assessing the results of this operation and will provide additional information as and when appropriate," Army Colonel Steve Warren, a Pentagon spokesman, told reporters.

Warren said the operation took place on Thursday about 150 miles (240 km) west of Mogadishu near the town of Dinsoor. He said it was aimed at a "high-value target" but declined to name the individual or specify how it was carried out, other than to say no U.S. troops were on the ground in Somalia.

Dinsoor is not far from the village of Abaq Xaluul, where residents reported on Thursday that a drone attack about sunset killed three al Shabaab members.

"I was on the outskirts of Abaq Xaluul village when a car drove past me and soon I heard the huge blast from a drone ahead of me," resident Hussein Nur told Reuters by telephone.

"I saw the car and the three men on board completely burnt and then many armed al Shabaab fighters driving in cars reached the scene," he said.

Other residents gave similar accounts. Al Shabaab had no immediate comment. The United States previously has targeted senior leaders of the group with drone strikes.

Last year, an unmanned U.S. aircraft killed al Shabaab leader Ahmed Godane, forcing the group to appoint a new chief. Last month, a U.S. missile strike killed Yusef Dheeq, blamed for masterminding attacks at home and abroad.

(Reporting by David Alexander; Additional reporting by Abdi Sheikh and Feisal Omar in Mogadishu; Editing by Lisa Shumaker)