The deployments include expanded land-based Patriot defensive missile installations in Kuwait, Qatar, UAE and Bahrain, as well as Navy ships with missile defence systems within striking distance in and around the Mediterranean, officials said.
General David Petraeus, who as head of US Central Command is responsible for military operations across the Middle East, said this month that the United States has stationed eight Patriot missile batteries in four Gulf countries, which he did not identify.
The build-up began under the Bush administration, but has expanded under President Barack Obama, who is pushing for a new round of sanctions against Iran over its nuclear program.
Officials said the expansion was meant to increase protection for US forces and key allies in the Gulf.
The chairman of the US military's Joint Chiefs of Staff, Admiral Mike Mullen, said last month the Pentagon must have military options ready to counter Iran should Obama call for them.
"The chairman has made it clear many times that he remains concerned about the ballistic missile threat posed by Iran, but it would be inappropriate to discuss any mitigation or defense measures we might have in place to deter/defeat that threat," a spokesman for Mullen said.
Obama announced a revised missile defense system last year that included the deployment of Aegis ships equipped with missile interceptors to help defend Europe and US forces against Iranian rockets.
The Pentagon said it envisioned keeping three ships at any given time in and around the Mediterranean and the North Sea to protect areas of interest, with the possibility of sending additional ships to the region as needed.
The Obama administration said the decision to change plans was based mainly on technological developments and a shift in intelligence assessments to meet short- and medium-range missile threats posed by Iran.
Pentagon officials said deploying ships with SM-3 interceptors, made by Raytheon Co., would provide the flexibility to move US missile defence capabilities as may be needed.
Ships with Aegis interceptor systems are capable of blowing up ballistic missiles above the atmosphere. The system can track over 100 targets, military officials said.
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