Image caption Many in Pakistan say that the strikes cause indiscriminate deaths and injuries

CIA drone attacks in Pakistan are responsible for unlawful killings, some of which could amount to war crimes, Amnesty International says.

Amnesty said it reviewed nine recent drone strikes in North Waziristan and found a number of victims were unarmed.

In a separate report looking at six US attacks in Yemen, Human Rights Watch says two of them killed civilians at random, violating international law.

Drone warfare has become common in the US pursuit of al-Qaeda and the Taliban.

Few details are known about the covert US drone operation.

Senior al-Qaeda and Taliban leaders have been killed in drone strikes in Pakistan, but civilians have also died.

These attacks cause outrage in Pakistan, where many assert that the strikes cause indiscriminate deaths and injuries.

Last week, a UN investigation found that US drone strikes had killed at least 400 civilians in Pakistan, far more than the US has ever acknowledged.

UN special rapporteur Ben Emmerson accused the US of challenging international legal norms by advocating the use of lethal force outside war zones.

Establishing precise casualty figures and identifying the dead in such attacks is virtually impossible as independent media are barred from tribal areas near the Afghan border.

'Very tight leash'

Analysis The new Amnesty International report has sought to document more evidence of civilian deaths in drone strikes than before, but some of the cases they have brought forth as examples were already known to the media. As for local claims of civilian deaths in strikes targeting militant camps, they are almost impossible to prove. One reason is the restricted media access in the region. The other is the militants' tendency to cordon off the targeted sites and make quick burials. But Waziristan is a small place, with well-knit tribal clans living and interacting closely with each other. Civilian deaths cannot go unnoticed here, and anecdotal evidence travels fast. The general impression that one gets from talking to elders and correspondents from the area is that drone strikes are for the most part accurate, causing little or no collateral damage. They say if civilians deaths had been as high as those mentioned in some recent international reports, there would have been more of an outcry against it both socially and also in the media.

Amnesty said it had investigated nine of 45 recently reported attacks by US drones, unmanned aircraft operated remotely in control rooms, often on other continents.

The group called on the US to disclose information and the legal basis for strikes carried out in Pakistan.

In the report, Will I Be Next? US Drone Strikes in Pakistan, the rights group named several victims who, it says, had been unarmed and "posed no threat to life".

In October 2012, 68-year-old grandmother Mamana Bibi was killed in a double strike as she picked vegetables in the family's fields while surrounded by her grandchildren, said the report.

It said US President Barack Obama's pledge earlier this year to increase transparency around drone strikes had not been fulfilled.

"This secrecy has enabled the USA to act with impunity and block victims from receiving justice or compensation. As far as Amnesty is aware, no US official has ever been held to account for unlawful killings by drones in Pakistan," the report said.

It called on the governments of Pakistan, Australia, Germany and the UK to investigate drone strikes or other abuses that may constitute human rights violations.

Meanwhile, Human Rights Watch said in its report that six US drone attacks in Yemen killed 82 people, including at least 57 civilians.

It added that two of the strikes killed innocent people indiscriminately.

A controversial aspect of the US policy is that drone attacks are carried out not by the military but by the Central Intelligence Agency.

US Defence Secretary Leon Panetta has argued in favour of the policy, saying that the US will continue to defend itself.

President Obama has insisted the strategy was "kept on a very tight leash" and that without the drones, the US would have had to resort to "more intrusive military action".