Britain has been accused of blocking the UN inquiry into atrocities in Yemen allegedly carried out by its theocratic ally Saudi Arabia.

In an open letter to the UN Human Rights Council (HRC), a group of NGOs has alleged that the UK is blocking the progress of the inquiry by failing to give backing to an effort by the Netherlands to set up a full investigation.

Since the conflict began the UK has sold more than £3 billion (US$3.9 billion) in arms to the Saudi regime and provided training on targeting both by warplanes and artillery.

The groups, including Human Rights Watch and Campaign Against the Arms Trade (CAAT), have said that the inquiry would “establish the facts, collect and preserve information related to violations and abuses with a view to ensuring that those responsible for crimes are brought to justice in fair trials.”

The letter, which was coordinated by the medical peace group Medact, puts a powerful case for a proper examination of allegations.

“As health professionals, we have a duty to speak out against all causes of ill health in Yemen. This must include the sale and export of UK weaponry that is fueling the conflict.”

Speaking for his organization, CAAT’s media head Andrew Smith said: “For 18 months now, UK arms have been central to the destruction of Yemen.

“The aid that is being given amounts to a small fraction of the damage that has been caused and pales in comparison to the £3.3 billion worth of arms that have been licensed.”

He called for Prime Minister Theresa May and Foreign Secretary Boris Johnson to “end the arms sales and put a stop to the uncritical support that the UK provides for the Saudi regime.”

Johnson last week claimed that the UK was “using a very, very wide variety of information sources about what is happening to acquaint ourselves with the details” of events in the war-torn country.

Saudi Arabia has been fighting Shiite Houthi rebels in Yemen since 2015. Estimates for those displaced by the war are around 2.5 million while 50 percent of the population are reported to be suffering from malnourishment.