US envoy Richard Olson was informed about the concerns by Sartaj Aziz, the Prime Minister's Advisor for National Security and Foreign Affairs, soon after the attack yesterday, the Foreign Office said.
"The deep concerns were conveyed to the US Ambassador in Islamabad on the same day by the Advisor to the Prime Minister for National Security and Foreign Affairs," it said in a statement.
"The government demands immediate cessation of these drone strikes," it said.
Prime Minister Nawaz Sharif had raised the issue with President Barack Obama and other US leaders during his recent visit to Washington.
"It was therefore a matter of particular concern to Pakistan that the November 21 strike targeted a location in the Khyber-Pakhtunkhwa province and also resulted in the unfortunate killings of several persons including children," it said.
Reports from Hangu district, where the drone targeted a seminary, said three commanders of the dreaded Haqqani network were among the six persons killed.
Yesterday's attack was the first since the one that killed Tehrik-e-Taliban Pakistan chief Hakimullah Mehsud on November 1.
It came a day after Aziz told a parliamentary panel that the US had given Pakistan an assurance that drone attacks would not be carried out during negotiations with militants.
