Updated

Two American missile attacks killed 15 people Friday in a region in northwest Pakistan that has seen few such strikes in the past, Pakistani officials said, in an apparent expansion of the CIA-led covert war inside the country.

The strikes took place in two villages in the Tirah Valley in the Khyber region, the Pakistani intelligence and government officials said. The same valley, which is known to be home to militants, was hit late Thursday in another U.S. attack.

The two intelligence and two government officials spoke on condition of anonymity because they were not authorized to speak to the media.

Most of the more than 100 missile attacks this year inside Pakistan have taken place in North Waziristan, a tribal area effectively under the control of Taliban and al-Qaida groups.

Pakistani officials protest the strikes, but are believed to have secretly authorized at least some of them. Analysts also say targeting information for many of the attacks is likely to be provided by Pakistani intelligence officials.

The missiles, fired from unmanned drones, hit houses in the villages of Speen Drang and Shandana, the officials said. It was unclear exactly how many people were killed in each respective village.

The missile attacks have been credited with killing many top militants, but have stirred nationalist anger in Pakistan.

The frequency of the attacks has more than double this year compared to last, suggesting the Obama administration sees the tactic as a key to reducing the strength of militants planning attacks in Afghanistan and the West.