British Prime Minister Theresa May has called upon Saudi Arabia to ease the siege on Yemen as a matter of urgency to avert a humanitarian catastrophe. The statement, published by May's office yesterday, said the British leader met King Salman and Crown Prince Mohammed bin Salman late on Wednesday during her three-day tour of the Middle East. <br/><br/>They discussed Yemen, where the prime minister made clear that the flow of commercial supplies on which the country depends must be resumed to avert a humanitarian catastrophe, the statement said.