UN official says drone attacks violate Pakistan's sovereignty and Obama administration has repeatedly been told to stop

US drone attacks on Pakistan's tribal districts are carried out without the consent of the government in Islamabad and are a violation of its sovereignty, a UN official has warned.

Returning from a three-day visit to the country's capital, Ben Emmerson QC, the UN's special rapporteur on counter-terrorism and human rights, said he had been given assurances that there was no "tacit consent by Pakistan to the use of drones on its territory".

His comments on Friday are a direct response to widespread suspicions that some parts of Pakistan's military or intelligence organisations have been providing clandestine authorisation to Washington for attacks by unmanned aerial vehicles (UAVs) on Taliban or al-Qaida suspects in provinces on the Afghan border.

Emmerson said he had been told that "a thorough search of Pakistani government records had revealed no indication of such consent having been given".

His statement said that Pakistan's foreign affairs ministry had confirmed "that since mid-2010 (and to date) it has regularly sent 'notes verbales' to the US embassy in Islamabad protesting the use of drones on the territory of Pakistan" and "requiring the US to cease these strikes immediately".

Pakistan also released updated casualty estimates from US drone attacks.

Officials told Emmerson, a London-based barrister, that Pakistan believed there have been at least 330 drone strikes on its territory since 2004.

Islamabad's records showed that about 2,200 deaths had been caused by drone strikes and a further 600 people had suffered serious injuries.

The difficulty of reaching mountainous regions and the Pashtun tribal practice of burying the dead as soon as possible made collecting precise figures difficult, government officials admitted.

Of those who died, at least 400 were said by the government to have been civilians and a further 200 were regarded as probable non-combatants.

Emmerson's high-profile investigations have forced the Obama administration to respond to mounting international concerns about its drone attacks in Pakistan, Yemen and Somalia.

US officials have defended their strikes as permissible as part of the administration's global "war on terrorism".

Speaking at the end of his visit, Emmerson said: "The position of the government of Pakistan is quite clear. It does not consent to the use of drones by the United States on its territory and it considers this to be a violation of Pakistan's sovereignty and territorial integrity.

"As a matter of international law the US drone campaign in Pakistan is therefore being conducted without the consent of the elected representatives of the people, or the legitimate government of the state. It involves the use of force on the territory of another state without its consent and is therefore a violation of Pakistan's sovereignty.

"Pakistan has also been quite clear that it considers the drone campaign to be counter-productive and to be radicalising a whole new generation, and thereby perpetuating the problem of terrorism in the region.

"Pakistan has called on the US to cease its campaign immediately. In a direct challenge to the suggested legal justification for these strikes, the government of Pakistan has also made it quite clear during these discussions that any suggestion that it is 'unwilling or unable' to combat terrorism on its own territory is not only wrong, but is an affront to the many Pakistani victims of terrorism who have lost their lives."