U.S. drone strikes in Pakistan killed two leaders of Al Qaeda's South Asia branch earlier this year, a spokesman for the militants said Sunday, confirming a major blow to the affiliate only months after its creation.

In an audio message, spokesman Usama Mahmood said a Jan. 5 drone strike in North Waziristan killed Ubaidullah, who was in charge of the group's Afghan affairs, while a later strike killed deputy chief Raja Suleman. He said both had fought under aliases. His claim corresponds with the dates of previously reported U.S. drone strikes in Pakistan's tribal region near the Afghan border.

Mahmood said Suleman graduated from Islamabad's International Islamic University and that Ubaidullah was from Pakistan's central city of Multan.

Mahmood also lashed out at Pakistan over a military offensive launched last summer in North Waziristan, along the Afghan border.

"This operation is being carried out under direct supervision of American forces, its leadership, and with their direct help through drones and jets," Mahmood said. "Pakistan's army is in fact just providing intelligence against the targets America wants to hit."

Mahmood said U.S. drone strikes had killed some 50 members of his group, known as Al Qaeda in the Indian Subcontinent. Pakistani officials had no immediate comment on the claims.

The CIA's drone program has killed Al Qaeda leaders, Pakistani Taliban fighters and other militants hiding in its tribal regions, but has stoked anger across Pakistan over allegations of widespread civilian casualties. Since 2004, the U.S. has carried out some 400 suspected drone strikes in the country, according to the New America Foundation's International Security Program, which tracks the American campaign.

Al Qaeda leader Ayman al-Zawahiri announced the creation of the South Asia affiliate in September. Al Qaeda increasingly finds itself overshadowed internationally by the Islamic State group, which holds a third of Iraq and Syria in a self-declared caliphate.

The Pakistani army said Sunday that troops surrounded a group of militants trying to enter from Afghanistan, killing 10 of them in an ensuing gunbattle.