Pakistani security officials say gunmen have killed a Pakistani Taliban commander in the country's northwest tribal region.

Shakirullah Shakir was reportedly riding a motorcycle near Miran Shah, the main town in North Waziristan, when he was gunned down by assailants.

Pakistani officials say they do not know why Shakir was killed. He was affiliated with the Fidayeen-e-Islam wing of the Pakistani Taliban, which helped carry out the militant group's suicide attacks.

Meanwhile, in neighboring South Waziristan on Monday, intelligence officials say two separate U.S. drone strikes killed at least 20 suspected militants.

Pakistani intelligence officials say the first strike hit a vehicle near the Afghan border, killing eight suspected militants. Hours later, missiles hit a compound believed to be a militant training center in the town of Mantoi, killing 12.

The area is a known stronghold for Pakistani Taliban and al-Qaida-linked militants and has been repeatedly targeted by missiles fired from pilotless aircraft in recent months.

The United States does not publicly acknowledge the drone strikes, which are believed to be carried out with the help of Pakistani intelligence. Pakistan publicly criticizes the attacks as a violation of its sovereignty.

On Monday, a senior commander of the Pakistani Taliban said he was splitting from the group to protest attacks against “innocent” and “unarmed” civilians.

Fazal Saeed, who had been serving as the leader of the Tehrik-e-Taliban in the Kurram tribal agency, said he would form a new militant group called Tehrik-e-Taliban Islami. He said the new group would focus its attacks on NATO troops in neighboring Afghanistan.

Saeed said he has repeatedly told leaders of the Pakistani Taliban that suicide bombings against mosques and other civilian targets must be stopped.

Thousands of civilians and police have been killed in such attacks claimed by the Taliban.

A Taliban militant and his wife reportedly carried out Saturday's attack on a police station in the northwestern town of Kolachi, killing at least 10 police officers.