DUBAI/MANILA — U.S. Secretary of State Marco Rubio said on Wednesday the United States is still willing to negotiate an end to the Iran crisis but Tehran is not serious about talks, as the widening conflict disrupted two of the world's most critical energy chokepoints. Rubio made his comments in a meeting of Southeast Asian foreign ministers a day after three oil tankers carrying Saudi crude to Asia reversed course in the Red Sea, apparently in response to threats from Yemen's Iran-aligned Houthis. The Houthis, who control the coast at the mouth of the Red Sea, announced a naval blockade on Saudi Arabia on Monday, opening a potential new front in the war which has killed thousands of people across the Gulf since it began on February 28 with U.S. and Israeli attacks on Iran. With Iran already threatening shipping through the Strait of Hormuz leading out of the Gulf, the Red Sea has served as the main alternate route out for millions of barrels of Saudi oil per day. A senior Iranian official told Reuters on Monday that Tehran had received a proposal from mediators for a 10-day ceasefir