The British government's arms sales to Saudi Arabia are unlawful, the United Kingdom's all-party committee of the House of Lords has concluded in a report.
The document, published on Saturday by the international relations select committee, also found that by sanctioning weapons exports to Riyadh, the British government has found itself on "the wrong side of the law" on the war in Yemen.
It said that these weapons are likely to be the cause of civilian casualties in the war-torn country, where Saudi Arabia, along with its allies, has been carrying out air raids against the Houthi rebels since March 2015.
The publication is the first from a parliamentary committee that has described the arms sales to Saudi Arabia as unlawful - and has said that ministers are not making independent checks to see if British arms being used are in breach of the law. Rather they are relying on questionable investigations by their Saudi allies.
"The government asserts that, in its licensing of arms sales to Saudi Arabia, it is narrowly on the right side of international humanitarian law.
"Although conclusive evidence is not yet available, we assess that it is narrowly on the wrong side: given the volume and type of arms being exported to the Saudi-led coalition, we believe they are highly likely to be the cause of significant civilian casualties in Yemen, risking the contravention of international humanitarian law," the report said.
The committee placed no legal obligation on ministers, but is likely to put pressure on Saudi Arabia and the United Arab Emirates (UAE) to resolve the crisis in Yemen through dialogue and halt military intervention.
Although a United Nations-brokered ceasefire in the port city of Hodeidah is holding, coalition air attacks continue to intensify across Yemen, as has fighting in other regions such as the Saudi-Yemeni border and the Saada governorate.
The country has faced six years of civil war, with heavy involvement from regional powers backing opposing sides, leaving the population on the brink of famine.
War broke out in 2013 after the Houthis took control of the capital, Sanaa, which led to a Saudi-led response, backed by the United States, to reinstate the internationally-backed government.
An estimated 8.4 million people in Yemen are at risk of severe famine and more than 22 million people, or 75 percent of the population, are in need of humanitarian assistance.
International pressure has been growing to end Western support for Saudi's involvement in Yemen as more than two million people have been displaced, and over 10,000 killed so far.
The war has resulted in a collapsed economy and a cholera outbreak that has affected more than 1.1 million people.