SINGAPORE/TOKYO (Reuters) – Brent crude oil shot up nearly 6 percent on Thursday after Saudi Arabia and its Gulf Arab allies began a military operation in Yemen, but the benchmark later came off its high near $60 as importers saw no immediate threat to supplies. The strike against Houthi rebels, who have driven the president from Yemen’s capital Sanaa, could stoke concerns about the security of Middle East oil shipments. The risk from the attack in Yemen was heightened because the Houthis have received some support from Iran, Saudi Arabia’s long-time rival for dominance in the Middle East.