Tension between the US and Iran heightened dramatically today with the disclosure that Barack Obama is deploying a missile shield to protect American allies in the Gulf from attack by Tehran. The US is dispatching Patriot defensive missiles to four countries — Qatar, United Arab Emirates, Bahrain and Kuwait — and keeping two ships in the Gulf capable of shooting down Iranian missiles. Washington is also helping Saudi Arabia develop a force to protect its oil installations. American officials said the move is aimed at deterring an attack by Iran and reassuring Gulf states fearful that Tehran might react to sanctions by striking at US allies in the region. Washington is also seeking to discourage Israel from a strike against Iran by demonstrating that the US is prepared to contain any threat.