Women were raped until they were unconsciousness, children were tortured and tens of thousands of people were forced from their homes in a "scorched earth" campaign ordered by one of Britain's closest allies in Africa, Ethiopia's prime minister Meles Zenawi.

"There has been a wilful blindness and conspiracy of silence on the part of Ethiopia's main donors, and a failure to condemn or even recognise these abuses," Georgette Gagnon, the rights group's Africa director, said in Nairobi today at the launch of a new report.

"Their silence amounts to complicity in crimes against humanity and war crimes carried out as a deliberate policy of the Ethiopian government." Britain gives Ethiopia more than £130 million in aid annually, part of the £1 billion the country receives from major Western donors including the US and the EU.

But at the same time, Mr Meles has overseen the intensification of a military campaign against ethnic Somali rebels operating in Ethiopia's eastern Ogaden region.

The previously low-level rebellion was met with a brutal armed response after the rebels attacked a Chinese oil installation in April last year, killing 70 Chinese and Ethiopian workers.

Since then, Human Rights Watch has documented the executions of more than 150 people, mass detentions, the widespread destruction of property and theft of livestock.

Satellite images published today show before and after pictures of villages razed to the ground.

The attacks, the rights group alleges, were carried out by the Ethiopian army in a bid to break civilian support for the Ogaden National Liberation Front, rebels who have been fighting for self-determination for Ethiopia's ethnic Somali region for more than 20 years.

"The soldiers started beating us with thick sticks," said one woman quoted in the 130-page report, titled Collective Punishment and released today.

"They beat me until I fell to the ground... while I was lying on the ground I was raped. I don't know how many men raped me. Other women were raped too.

"Others were strangled with a rope but they did not die. In our group we were shot. I was hit behind the left shoulder with a bullet." Bereket Simon, special adviser to Mr Meles, denied all allegations in the report, telling the Associated Press, "It's not true. It's the same old fabrication."

British diplomats and Foreign Office officials are failing to press Ethiopia to stop the abuses, one senior Human Rights Watch researcher told The Daily Telegraph today.

"We have tried to raise this many times, but each time we are met with a very unpleasant reaction from the British," he said.

"They just don't want to know. They have convinced themselves that Ethiopia is the key to regional stability in the Horn of Africa, and they will stick to that line no matter what the government is actually doing to its own people."

A Foreign Office spokesman said: "We have seen the report and are concerned by many of the statements given and the allegations of human rights abuses in Ethiopia's Somali region.

"We have raised human rights issues with the government of Ethiopia on a number of occasions and have pressed for an independent investigation into these allegations."