An arms watchdog on Monday urged major weapons exporters, including the United States and France, to cut sales to Saudi Arabia over its actions in Yemen, as a conference on global arms trade opened in Geneva.

The World Trade Organization is hosting the second conference on the Arms Trade Treaty (ATT), which came into force in 2014 laying out new rules governing the international arms market.

By continuing to sell weapons to Saudi Arabia, which has led a 17-month-long campaign against rebels in Yemen, major weapons exporters that signed the ATT are guilty of "the worst kind of hypocrisy," said Anna Macdonald, director of the watchdog Control Arms.

"The ATT has been in force for nearly two years but some States Parties are violating it with impunity," Macdonald added in a statement.

"Every day, we are seeing the devastating impact of the sale of arms and ammunition for use on civilians in Yemen."

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

Saudi Arabia has faced fierce criticism over its Yemen offensive in support of the internationally recognised government of President Abedrabbo Mansour Hadi.

There have been repeated strikes on civilian targets. Medical charity Doctors Without Borders (MSF) has described the Saudi-led coalition bombings as "indiscriminate."

France authorised $18 billion (16 billion euros) in weapons sales to Saudi Arabi last year, Control Arms said in a report this month.

The United States approved arms deals with Riyadh worth $5.9 billion in 2015, while for Britain the figure was $4.0 billion.

France and Britain have ratified the ATT. The US has signed the deal, but Congress has not approved it.

Control Arms accused those countries of "flouting international law in plain sight by continuing to sell billions of dollars worth of deadly weapons to Saudi Arabia."

The US Navy announced Saturday it had slashed the number of intelligence advisers directly supporting the Saudi-led coalition's air war in Yemen following concerns over civilian casualties.