"It is highly regrettable that a jirga (tribal assembly) of peaceful citizens, including elders of the area, was carelessly and callously targeted with complete disregard to human life," Gen. Ashfaq Parvez Kayani, who holds the highest post in the Pakistani army, said in a statement.
The Obama administration had no official response. Washington does not publicly acknowledge the covert CIA drone program, which was started in 2004.
Pakistani officials said several missiles fired from U.S. drones killed 26 of 32 local and Taliban representatives meeting in the mountainous North Waziristan region near Afghanistan to settle a chromite mine dispute.
Eleven of the dead were Taliban fighters -- two Taliban fighters survived -- but the rest were elders and locals not tied to the militants, Pakistani officials said.
Most reporters are barred from visiting the region, so it is difficult to independently confirm who was killed.
The attacked Datta Khel region of North Waziristan is an al-Qaida and Taliban Islamist militia stronghold and U.S. drones have regularly attacked it since October 2008, a United Press International accounting indicates.
Thursday's strikes were the second such barrage in two days there and the sixth in the tribal areas in the past week, said The Long War Journal online news site, which monitors the Afghanistan and Pakistan wars.