Fifty-seven rights groups from around the world on Tuesday demanded a United Nations inquiry into abuses in Yemen, where an escalating conflict has killed thousands and fueled a humanitarian crisis.
Yemen, the Arab world's poorest country, has been wracked by violence since Houthi rebels and their allies seized vast tracts of territory, including the capital, Sanaa.
The conflict escalated when a Saudi-led coalition intervened in 2015, exacerbating the crisis that has left millions on the brink of famine and hundreds of thousands suffering from cholera.
In a letter to members of the UN Human Rights Council, the 57 signatories called for the creation of an independent body to look into violations and abuses of international human rights and humanitarian laws.
"Serious violations of international humanitarian law and violations and abuses of international human rights law by parties to the conflict have continued to be committed with impunity," said Human Rights Watch (HRW), one of the signatories.
HRW said in a statement that the Saudi-led coalition had conducted scores of "unlawful air strikes, some of which may amount to war crimes that have killed thousands of civilians and hit schools, hospitals, markets and homes".
It added that Houthi rebels and forces loyal to former President Ali Abdullah Saleh "have fired weapons indiscriminately ... killing and maiming scores in attacks that may amount to war crimes".
Since 2015, the UN High Commissioner for Human Rights had been calling for investigations into alleged violations and abuses in Yemen, it noted.
"The victims of abuses in Yemen cannot afford to wait longer for credible investigations into ongoing grave violations and abuses to be undertaken," said the letter.
In an interview with Al Jazeera, Lynn Maalouf, Middle East research director at Amnesty International, which also signed the letter, said human rights groups operating in Yemen have been documenting abuses from all sides of the conflict since March 2015.
"What we have known since the armed conflict began is that serious violations are happening every day, as we speak," she said in Lebanon' capital, Beirut.
"Just last week, there was a Saudi-led coalition air strike that killed an entire family of eight people - five of these people were children. The Saudi-led coalition said there was a technical error but these violations are happening again and again."
Maalouf also said that human rights groups are becoming increasingly frustrated with not being able to access the country.
"The coalition is making it more difficult for journalists and internatinal organisations to be on the ground in Yemen and to continue doing our documentation work," she said.
"This makes it all the more urgent for member states at the Human Rights Council when they meet next week in Geneva to heed the calls of our organisations for an independent, international and impartial investigative body."
More than 10,000 people have been killed and 40,000 wounded since the Saudi-led coalition intervened to support the internationally-recognised government of President Abd-Rabbu Mansour Hadi.
The UN has called Yemen the "largest humanitarian crisis in the world".
Cholera epidemic decline
Close to 2,000 Yemenis have also died of cholera since April and another 600,000 are expected to contract the infection this year.
However, a UNICEF statement on Tuesday said that the cholera epidemic has been declining for the past two months because of an unprecedented response by "unsung local heroes".
The UNICEF statement said that the efforts of thousands of local volunteers backed up by UN agencies has resulted in the weekly number of suspected new cases of cholera falling by a third since the end of June.