ISLAMABAD Pakistan on Monday strongly condemned a jump in U.S. drone strikes on its territory, using language that could increase tension between strategic allies already in dispute over military supply routes for NATO that Pakistan has closed.
Three drone strikes in as many days on suspected militants have killed 27 people, Pakistani intelligence officials say.
The foreign ministry called the attacks "illegal" and said they violated the South Asian country's sovereignty.
Washington and Islamabad are deadlocked in negotiations over the re-opening of overland supply routes to NATO forces in Afghanistan.
Islamabad blocked the supply routes in November after 24 Pakistani soldiers were killed by cross-border "friendly fire" from NATO aircraft.
The supply lines are considered vital to the planned withdrawal of most foreign combat troops from Afghanistan before the end of 2014.
The NATO attack plunged relations between Washington and Islamabad to their lowest point in years, and prompted Pakistani leaders to review ties.
Pakistan's parliament called for an end to U.S. drone strikes, and the foreign minister told Reuters in an interview in April that the United States was ignoring Islamabad's demands for an end to the operations.
Publicly, Pakistani officials condemn the use of the drones, saying they violate Pakistan's sovereignty and warning the Americans they are driving angry Pakistanis into the arms of militant groups.
But analysts say successful drone strikes, especially those that kill senior militants, would not be possible without help from Pakistani intelligence agencies.
It is not clear how much intelligence the two sides have shared in recent months.
The recent drone strikes have focused on the North Waziristan tribal area near the Afghan border. U.S. officials believe members of the Haqqani network, one of the most dangerous Afghan insurgent groups, is based there.
The unruly area is also home to members of al Qaeda.
U.S. officials say such strikes by the remotely piloted aircraft are a highly effective way of attacking militants and an important weapon in the war against militancy.
In one of the most high-profile attacks, Pakistani Taliban leader Baitullah Mehsud was spotted on the rooftop of his father-in-law's house in a village in South Waziristan in 2009.
Live video feeds showed Mehsud, who had health problems, on an intravenous drip. Predator Hellfire missiles then killed the Pakistani state's top enemy.
The Obama administration has stepped up drone strikes and termed them legal under international law.
The aerial campaign is one of several sticking points in talks aimed at repairing relations, which have deteriorated sharply after a series of events including the secret U.S. raid that killed Osama bin Laden in Pakistan last year.
(Editing by Michael Georgy and Tim Pearce)