Security sources said there was strong evidence that Taj Gul Mehsud, a senior Taleban commander and close aide to Tehreek-e-Taleban Pakistan (TTP) leader Hakimullah Mehsud, was among the victims in the attack on Wednesday.

Tribal elders from the Mehsud tribe in Mir Ali in neighboring North Waziristan said two missiles struck a militant compound. They put the death toll much higher - up to 22 people — and said all were members of the TTP, or Pakistan Taleban.

Six others were injured, security forces said.

Security officials and Taleban sources said the remote location of the suspected strike prevented it from being reported earlier, and reports of the strike only surfaced when the injured arrived at a hospital in Mir Ali.

The Obama administration has stepped up drone strikes against Al-Qaeda and Taleban militants in Pakistan’s tribal border areas in an effort to stabilize Afghanistan before the end of 2014, when all NATO combat troops are due to leave.

Wednesday’s strike came a day before another drone attack on Thursday killed five commanders of a powerful Pakistani Taleban faction that attacks Western forces in Afghanistan, one of the group’s leaders told Reuters.

The commanders killed in the strike belonged to the Maulvi Nazir faction of Pakistan’s Taleban, which carries out cross-border attacks from its strongholds in South Waziristan.

The Nazir faction threatened in June to escalate attacks on US troops in the NATO-led coalition in Afghanistan in response to intensified drone strikes on its territory.

South Waziristan is one of seven tribal agencies in the northwest in a region of Pakistan seen as a global hub for militants. Forbidding terrain makes the region an ideal spot for militants to train and plot attacks.

The spokesman for the TTP could not be reached for comment.