UK government arms sales to Saudi Arabia are lawful, the High Court has ruled, after seeing secret evidence.
The court rejected campaigners' claims ministers were acting illegally by not suspending weapon sales to the kingdom, which is fighting a war in Yemen.
The UN claims strikes on Houthi rebels caused thousands of civilian deaths.
The government said defence exports would continue to be reviewed but the Campaign Against the Arms Trade said an appeal against the ruling was planned.
The group had claimed the UK has contravened humanitarian law and attacked the refusal of the Secretary of State for International Trade to suspend export licences for the sale or transfer of arms and military equipment.
Lord Justice Burnett and Mr Justice Haddon-Cave, sitting in London, said the decision to carry on the arms trade was not unlawful.
The judges said "closed material", which had not been made public for national security reasons, "provides valuable additional support for the conclusion that the decisions taken by the secretary of state not to suspend or cancel arms sales to Saudi Arabia were rational".
'Very disappointing'
Equipment sold to Saudi Arabia includes Typhoon and Tornado fighter jets, as well as precision-guided bombs.
The sales contribute to thousands of engineering jobs in the UK, and have provided billions of pounds of revenue for the British arms trade.
Saudi Arabia has been supporting Yemen's internationally-recognised government after a civil war broke out in 2015.
Yemen crisis: Who is fighting whom?
Houthi rebels, loyal to deposed president Ali Abdullah Saleh, began an attack in 2014, forcing leader Abdrabbuh Mansour Hadi to flee the country for a time.
Since then the Saudi kingdom, and eight other mostly Sunni Arab states, have supported an air campaign aimed at restoring Mr Hadi's government.