JALALABAD, Pakistan — The Pakistani government on Monday strongly condemned a pair of NATO airstrikes on Pakistani soil that NATO officials said killed about 55 suspected insurgents over the weekend.

“These incidents are a clear violation and breach of the U.N. mandate” that governs the conduct of the U.S.-led international force in Afghanistan, the Pakistani Foreign Ministry said in a statement.

The airstrikes, which military officials said were carried out to beat back an attack on a small Afghan army border outpost, come amid what Pakistani officials describe as a sharp rise in suspected CIA drone attacks targeting Taliban sanctuaries in Pakistan.

Although NATO troops have occasionally crossed into Pakistan while pursuing militants, this weekend’s operation was unusual for the high death toll and Islamabad’s sharp rebuke.

The incident is likely to exacerbate tensions between the U.S-led international force in Afghanistan and Pakistan, which Washington sees as a crucial, if sometimes unreliable, partner in the war in Afghanistan.

Maj. Michael Johnson, a NATO spokesman, said NATO helicopters entered Pakistani airspace after Combat Outpost Narizah in Khost province came under attack Friday.

He said 49 suspected insurgents were killed in the initial engagement.

A second team of attack helicopters was dispatched to the location Saturday morning to relieve the initial team, Johnson said. Pilots from the second crew opened fire after they came under attack from fighters on the ground, Johnson said. He said an “additional four to six” suspected insurgents were killed in the second airstrike.

“The rules of engagement were followed,” Johnson said. “They were acting in self-defense.”

Johnson said NATO has not received reports suggesting civilians may have been caught in the fire.

Islamabad often protests suspected U.S. airstrikes on Pakistani soil, but Pakistani officials are widely believed to have given the U.S. approval to pursue militants along tribal regions not under government control where many al-Qaida and Taliban leaders operate.

NATO officials say they have permission to target militants in Pakistan when they are acting in self-defense.

The Pakistani Foreign Ministry statement denied that.