WASHINGTON - Yemeni President Ali Abdullah Saleh arrived in the United States for medical treatment on Saturday, a week after leaving Yemen for Oman under a plan for him to step down to end a year of protests against his rule.US State Department spokesman Noel Clay confirmed his arrival."We expect he will stay here for the time that corresponds to his treatment," Clay said. He declined to give any further details.In London, a Foreign Office official said Saleh's plane had stopped at a British airport en route to the United States.Yemen's state news agency said he had left the Omani capital Muscat, his home for the past week, to receive medical treatment.Saleh has transferred some powers to his deputy and enjoys immunity from prosecution under a deal meant to end increasing instability in Yemen.The deal also established a transitional government including the opposition and envisions restructuring Yemen's armed forces, important units of which are led by Saleh's relatives.The United States, which endorsed the plan to coax Saleh out of office by granting him immunity from prosecution over the deaths of protesters, had defended its decision to issue him a visa, despite criticism that it would be seen as sheltering him.Saleh was the target of an apparent assassination attempt in June. The bombing of his presidential compound covered him with severe burns and drove him abroad to recover in neighboring Saudi Arabia. He returned to Yemen in September.