A report by the United Nations Human Rights Council has called for independent investigations to be carried out into drone attacks after a series of strikes that result in unexpected civilian deaths in Afghanistan, Pakistan, Yemen and elsewhere. Most of the attacks involved US drones.

In a 21-page report, the UN special rapporteur on human rights, Ben Emmerson, records a dramatic reduction in drone strikes in 2013 in Pakistan but increases in Afghanistan and, towards the end of the year, in Yemen.

The decline in drone strikes in Pakistan comes after its government's repeated calls for the US to reduce their number. Islamabad argued that the impact of drone strikes was counterproductive, turned opinion in the country against the US and undermined the Pakistani government.

But Emmerson noted a threefold increase in recorded civilian casualties from drone strikes in Afghanistan in 2013. He concluded that states have an obligation to launch inquiries into cases in which civilians become caught up.

His report said: "Having regard to the duty of states to protect civilians in armed conflict, the special rapporteur concluded that in any case in which there have been, or appear to have been, civilian casualties that were not anticipated when the attack was planned, the state responsible is under an obligation to conduct a prompt, independent and impartial fact-finding inquiry and to provide a detailed public explanation of the results.

"This obligation would be triggered whenever there is a plausible indication from any apparently reliable source that unintended civilian casualties may have been sustained."

The proposal is likely to form the basis for a draft resolution to be debated by the UNHRC in Geneva, Switzerland.

Emmerson devoted a large part of the report to listing specific drone strikes involving civilians. He said he had identified 30 attacks out of a total of 37 brought to his attention in which civilians had been killed, suffered life-threatening injuries or been put at risk.

In Afghanistan, Emmerson, who travelled widely for the report, said that up to the end of 2012 drone strikes "appeared to have inflicted significantly lower levels of civilians casualties than aerial attacks carried out by other air platforms. This is no longer the position."

In 2013, drone attacks accounted for 40% of the total number of civilian fatalities from air strikes. There were 45 civilian fatalities and 14 non-fatal injuries, a threefold increase compared with 2012.

In Pakistan, he recorded "a marked drop" in civilian casualties since 2012. "Figures to the end of 2013 confirm that there has been a significant de-escalation in the number of recorded drone strikes in Pakistan," he said. Strikes were down to 27 in 2013 from a peak of 128 in 2010, and for the first time in nine years there had been no civilian casualties reported.

"At the time of writing, there have been no reported drone strikes during 2014, the longest pause since President Obama took office," Emmerson said.

The Bureau of Investigative Journalism, which monitors media reports on drones strikes, reported last month that there had been no known drone strikes in Pakistan since 25 December. US officials say the lull was a response to requests by the Pakistani government, which has been trying to launch peace talks with the Pakistani Taliban.

In Yemen, Emmerson was told that the US routinely sought prior consent for attacks, although Human Rights Watch has quoted the Yemeni government as saying they were not pre-approved.

In Israel, he said the government stressed it aimed for zero civilian casualties, saying it provided advance warning of attacks where possible. But Emmerson "identified a number of sample strikes in which there are credible allegations that civilians were killed or injured as the result of Israeli drone strikes in Gaza".

Kat Craig, legal director of Reprieve, the legal charity which has been campaigning on the issue, said: "In Yemen, Pakistan and elsewhere, the US, assisted by its European allies, is carrying out devastating attacks with total impunity – a practice that is terrorising local communities, and creating far more extremism than it has ever eliminated.

"It is high time that the US provided full accountability and transparency around its use of drones, and investigated civilian casualties. This report will only increase pressure on the US to bring their covert programme out of the shadows."