UNITED NATIONS - A major arms watchdog Monday denounced some signatories and parties to the Arms Trade Treaty (ATT), including France and the United States, saying they were violating the treaty by selling vast amounts of weapons to Saudi Arabia that are being used to hit civilians in Yemen.

“Every day, we are seeing the devastating impact of the sale of arms and ammunition for use on civilians in Yemen,” Anna Macdonald, director of the watchdog Control Arms, told a news briefing as week-long UN negotiations began in Geneva aimed at putting teeth into the ATT which lacks a mandatory public reporting system for the $100 billion global arms trade. She added that countries like France, Britain and the United States have been “flouting international law in plain sight by continuing to sell billions of dollars worth of deadly weapons to Saudi Arabia.”

France authorized arms licenses worth $18 billion to Saudi Arabia last year, followed by the US at $5.9b and Britain’s $4 billion, the group said in its latest study.

Nigeria’s ambassador Emmanuel Imohe, who chairs the conference, said: “The allegation is quite grave and it should be of concern to everyone including the ATT secretariat itself.”

Medecins Sans Frontieres (MSF) said last week it was evacuating its staff from six hospitals in northern Yemen after a Saudi-led coalition air strike hit one of its hospitals, killing 18 people.

 The coalition says it does not target civilians and accuses the Houthi group that it is battling in Yemen of placing military targets in civilian areas. A body that the coalition set up to look into civilian casualties is investigating the MSF incident, among others.

The war has killed more than 6,500 people since it began 16 months ago and raised the prospect of famine in the Arab world’s poorest country.

Outcry over civilian casualties has led some members of the US Congress to push for restrictions on arms transfers. The Obama administration this month approved a potential $1.15 billion arms package for Saudi Arabia.

In a statement on Friday, the Pentagon cautioned that its support for Saudi Arabia in its campaign was not “a blank check,” however, and said it has pressed the coalition on the need to minimize civilian casualties.

Saudi Arabia started an air campaign against Yemen in March 2015 and later launched ground operations to undermine the ruling Houthi movement and its allies and restore power to Yemen’s resigned president, Abd Rabbuh Mansur Hadi.

Under the ATT, states are required to block any arms deal if they have knowledge at the time of the sale that the weapons will be used against civilians.

This comes as intentional aid groups and human rights organizations, which have operatives on the ground in Yemen, have confirmed multiple cases of Saudi airstrikes targeting civilians in the impoverished Arab country.