ISLAMABAD (AFP) – Pakistan has strongly condemned a drone strike against a Taliban bastion in the northwest tribal region that killed 35 people and demanded an apology and explanation from United States.

Civilians and police were among those killed Thursday when US missiles ploughed into a militant training compound in Datta Khel town, 40 kilometres (25 miles) west of Miranshah, the main town in tribal North Waziristan.

"The government of Pakistan strongly condemns the drone strike which has resulted in a large number of casualties," Pakistani foreign ministry spokeswoman Tehmina Janjua said in a statement Friday.

"Foreign Secretary Salman Bashir conveyed this strong condemnation to US ambassador Cameron Munter and has demanded an apology and explanation," she added.

She added Pakistan's ambassador to the US Hussain Haqqani had been asked to make a similar strong protest to the State Department.

It was the most lethal drone strike to hit the lawless region since August 2008 when the covert campaign escalated in the areas bordering Afghanistan, and the seventh such attack in nine days.

The prime minister condemned the attack as "irrational".

"Prime Minister Yousuf Raza Gilani has strongly condemned the drone attack ... and said it will only strengthen the hands of radical and extremist elements," an official statement said.

Army chief General Ashfaq Kayani and Syed Masood Kausar, the governor of Khyber-Pakhtunkhwa province, where the drone struck, also condemned the attack.

Kayani said the "unjustifiable" strike hit a council of tribal elders.

"It is highly regrettable that a jirga of peaceful citizens including elders of the area was carelessly and callously targeted with complete disregard to human life," he said, adding the army had protested "in the strongest possible terms".

Condemning the strike, governor Kausar said: "These attacks are against the sovereignty of Pakistan."

Although the drones operate with the tacit consent of Islamabad, Kausar said the government "will not tolerate such attacks".

Two security officials in Peshawar said that 35 people, mostly militants, were killed in the strike.

Two intelligence officials in Miranshah confirmed the toll.

"We have reports of a few civilian casualties, but most of those killed were local militants," one Miranshah official said.

"There were some civilians present inside the training centre. We were told that they came here to seek Taliban help to solve some of their disputes," a second intelligence official told AFP.

US drones have frequently targeted Datta Khel, known as a stronghold of the Taliban commander and Al-Qaeda-linked warlord Hafiz Gul Bahadar, and the Peshawar official said the militants hit were members of the Pakistani Taliban.

The drone strikes inflame anti-US feeling, which is running particularly high after authorities released a CIA contractor on Wednesday who had been held on suspicion of murder.

Missile attacks doubled in the area last year, with more than 100 drone strikes killing over 670 people in 2010 compared with 45 strikes that killed 420 in 2009, according to an AFP tally.

Most have been concentrated in North Waziristan, the most notorious Afghan Taliban and Al-Qaeda bastion in Pakistan, where the United States wants the Pakistan military to launch a ground offensive as soon as possible.

Pakistan says its troops are too overstretched to launch such an assault.

Thursday's attack came as small anti-US protests were held in various cities after a Pakistani court acquitted and freed Raymond Davis, a CIA contractor being held over the lethal shooting of two men in Lahore in January.

The case had badly hit shaky ties between Washington and Islamabad, as US authorities insisted Davis had diplomatic immunity from prosecution over the deaths and pressed for his release.

$2 million in blood money was finally paid to end the row, fixing a diplomatic rift but causing further resentment among the Pakistani public, who already see the covert US drone campaign as a breach of national sovereignty.

The United States does not confirm drone attacks, but its military and the Central Intelligence Agency (CIA) operating in Afghanistan are the only forces that deploy them in the region.