Pakistan is strongly condemning a series of U.S. drone strike that have killed at least 27 people in the last three days.

The foreign ministry issued a statement Monday saying “Pakistan has consistently maintained that these illegal attacks are a violation of its sovereignty and territorial integrity” and go against international law.

In the latest strike, Pakistani officials say missiles hit a compound in the Hesokhel village of the North Waziristan tribal agency early Monday, killing at least 15 people. There were reports that foreigners were among the dead. It was the deadliest drone strike since November of last year.

Two other suspected U.S. drone strikes hit the neighboring South Waziristan tribal district on Saturday and Sunday. Officials say Sunday's attack targeted a senior Taliban commander and killed 10 people. Saturday's strike killed two people.

The United States has ramped up its use of drones to target al-Qaida and Taliban-linked-militants in Pakistan's northwest, with eight attacks since May 23.

Washington considers drone strikes to be a vital tool in the war against al-Qaida and the Taliban.

Pakistan's foreign ministry said Monday that “the strategic disadvantages of such attacks far outweigh their tactical advantages, and are therefore, totally counterproductive.”

The recent drone strikes add to already tense relations between the United States and Pakistan.

The two countries have yet to reach an agreement on reopening NATO supply routes into Afghanistan. Pakistan shut down the supply lines after U.S. airstrikes mistakenly killed 24 Pakistani troops last November.

Pakistan's parliament has demanded a U.S. apology for the deadly cross-border attack and an end to the U.S. drone strikes.

Senior U.S. defense official Peter Lavoy is set to hold talks with Pakistani officials in Islamabad this week to try and break the deadlock over the supply routes.