The United States is boosting land and sea-based missile systems in and around the Gulf to counter what it calls a growing threat of an attack by Iran.
The deployments include more land-based Patriot surface-to-air missile installations in Kuwait, Qatar, the United Arab Emirates and Bahrain.
Seaborne missile defence systems are also being stationed in the Mediterranean.
The build-up began under the Bush administration but has increased under President Barack Obama who is pushing for a new round of sanctions against Iran over its nuclear programme.
US National Security Adviser General James Jones said: “We simply cannot afford a nuclear arms race in the Middle East as a consequence of Iran developing nuclear weapons and the ability to deliver such weapons.”
US defence experts believe there is a heightened risk that Iran could help facilitate attacks on Israel through Hezbollah in Lebanon and Hamas in Gaza in response to the prospect of international sanctions being applied to Tehran.