The letter read: "International humanitarian law obligates states that are parties to an armed conflict to investigate allegations of war crimes committed by their forces and bring those suspected of criminal responsibility to justice in fair trials. We are not aware of any [Saudi-led] Coalition members having done so".
The document, signed by numerous regional and international human rights groups, expressed its concern over the deaths of 2,000 people - mostly civilians - and warned on the humanitarian crisis being experienced in the country.
"The humanitarian situation continues to deteriorate with 21 million Yemenis - a staggering 80 percent of the population - in need of humanitarian assistance," the organizations warned.
The letter highlighted previous assertions made by the Human Rights Council, such as receiving information of indiscriminate and disproportionate attacks on densely populated areas.
Since May this year [2015], several reports from activists on the ground and human rights groups have shown that Saudi Arabia is using cluster bombs. This type of bomb fragments once it hits a target, carrying up to 200 smaller bombs inside.
Furthermore, journalists and independent observers have documented the large-scale destruction of complete neighborhoods and cities.
Additionally, a blockade imposed by the Saudi-led coalition remains in place and has prevented much-needed humanitarian aid from reaching Yemeni civilians.
