(CNN) -- A top American envoy was summoned by Pakistan's new government to protest a U.S. drone strike that killed at least six militants in the volatile North Waziristan province, the Pakistan government said Saturday.
U.S. charge d'affaires Richard Hoagland was summoned Friday at the order of Prime Minister Nawaz Sharif and given a letter of protest, the government said.
"Pakistan strongly condemns the drone strikes which are a violation of Pakistan's sovereignty and territorial integrity. The importance of bringing an immediate end to drone strikes was emphasized," it said in a written statement.
Drone strikes in the tribal regions bordering Afghanistan have drawn heated opposition in Pakistan because of civilian casualties.
"Obviously this is an issue that will be taken up at a higher political level with the American authorities," Sartaj Aziz, Pakistan's national security adviser, told reporters Saturday.
The issue of drone strikes is expected to be on the top of the agenda when U.S. Secretary of State John Kerry visits Pakistan later this month, he said.
The summoning of Hoagland came just two days after Sharif demanded in his inaugural address the U.S. stop its drone strikes. He reiterated the demand Saturday.
"We have protested many a time. This is simply unacceptable," Sharif said during a meeting with German Foreign Minister Guido Westerwelle, according to Pakistan state news.
But U.S. President Barack Obama defended the use of drone strikes last month, stopping short of directly commenting on the strikes in Pakistan.
Drone strikes were legal, Obama said, because the United States "is at war with al Qaeda, the Taliban and their associated forces."
Friday's drone strike follows a similar strike nearly two weeks ago that killed the Pakistan Taliban's second-in-command, Wali-Ur Rehman Mehsud.
Rehman was wanted by the United States on suspicion of being involved in the December 2009 suicide bomb attack that killed seven CIA employees at Forward Operating Base Chapman in Khost, Afghanistan, according to a publication by the U.S. National Counterrorism Center.
The drone strikes have only served to further roil U.S.-Pakistan relations, which flared following a 2011 raid by U.S. commandos on a compound in Abbottabad that ended with the killing of al Qaeda leader Osama bin Laden.