American military forces launched an operation in Somalia on Monday against the Qaeda-linked militant network the Shabab, defense officials said.

Rear Adm. John F. Kirby, the Pentagon press secretary, said that officials were still “assessing the results of the operation, and will provide additional information as and when appropriate.”

Admiral Kirby declined to go into further detail about the operation, which was first reported by CNN.

A senior American official, who asked not to be named because of the sensitivity of the operation, said it had been carried out with Somali partners against “a senior Shabab operative.”