Pakistan on Monday strongly condemned a series of U.S. drone strike that killed at least 27 people in the last three days.

The Foreign Ministry said in a statement that “Pakistan has consistently maintained that these illegal attacks are a violation of its sovereignty and territorial integrity and go against international law.”

Pakistani officials confirmed the dawn attack in the Hesokhel village of the North Waziristan tribal agency, in which at least 15 people were killed. They said the strike targeted militant leaders known to send fighters over the border in Afghanistan.

It was the deadliest drone strike since November of last year, and there were reports that foreigners were among the dead.

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 militants, while Saturday's strike killed another two.

Also Monday, police in the northwestern Pakistani city of Peshawar briefly detained three U.S. diplomats after weapons were found in their vehicle.

According to police the diplomats, accompanied by a Pakistani body guard and two drivers, were stopped for a routine check when police found several rifles, pistols and ammunition. Police said the Americans also had been questioned because they left Peshawar on a trip and returned without proper documents.

Relations between Washington and Islamabad have reached a new low over a series of events, including the killing of al-Qaida leader Osama bin Laden in Pakistan by U.S. special forces in May 2011 and an accidental killing of 24 Pakistani soldiers last November in a NATO air strike.

Pakistan's parliament has demanded a U.S. apology for the deadly cross-border attack and an end to the U.S. drone strikes. Washington refused, saying drone strikes are a vital tool in the war against al-Qaida and the Taliban. Islamabad responded by blocking NATO supply routes into Afghanistan and the two sides have yet to reach an agreement on reopening them.

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

The continued strikes could further sour diplomatic ties between the two countries, but there is no indication that Washington intends to stop them.

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.