A US attempt to shoot down a ballistic missile mimicking an attack from Iran failed after a malfunction in a radar built by Raytheon, the Defense Department said.

The abortive test over the Pacific Ocean coincided with a Pentagon report that Iran had expanded its ballistic missile capabilities and posed a "significant" threat to US and allied forces in the Middle East region.

The Missile Defense Agency said that in Sunday's test both the target missile, fired from Kwajalein in the Marshall Islands, and the interceptor, from Vandenberg Air Force Base in California, had performed normally.

"However, the Sea-Based X-band radar did not perform as expected," the agency said on its web site. Officials will investigate the cause of the failure to intercept, it said.

The SBX radar is a major component of the ground-based midcourse defense, the sole US bulwark against long-range missiles that could be tipped with chemical, biological or nuclear warheads.

It was the first time the US had tested its long-range defense against a simulated Iranian attack.

Previous drills have imitated a flight path from North Korea, another country in a standoff with the international community over its nuclear program.

The Pentagon's Ballistic Missile Defense Review released on Monday said Tehran had developed and acquired ballistic missiles capable of striking targets from the Middle East to Eastern Europe and had fielded increasing numbers of mobile regional ballistic missiles.

The Iranian program has received support in the past from Russia, China and North Korea, and Tehran still depends on outside sources for many missile components and parts, according to the Defense Intelligence Agency.

Defenses against Iran

To counter the Iranian threat, the United States has expanded land- and sea-based missile defense systems in and around the Gulf, according to US officials.

The deployments include expanded land-based Patriot defensive missile installations in Kuwait, Qatar, UAE and Bahrain, as well as Navy ships with missile defense systems in and around the Mediterranean, the officials said.

The Pentagon's Ballistic Missile report also singled out Syria's short-range missiles as a "regional threat". It said Damascus may have chemical warheads available for some of its missiles.

After Sunday's failed Pacific test, Raytheon and Boeing, which manages the overall system, had no immediate comment.

Harris Corp, which provides systems engineering for the SBX radar, said their technology was not involved.

Speaking at the Reuters Aerospace and Defense Summit in Washington in December, Army Lieutenant General Patrick O'Reilly, head of the Missile Defense Agency, said the test, costing about $150 million, would break new ground.

He described it then as "more of a head-on shot like you would use defending against an Iranian shot into the US." It was the first time such a scenario was being tested, he said.

Experts have compared the simulation to a bullet hitting another bullet in space. O'Reilly said the goal was to destroy the target over the north central Pacific when the missiles had a combined closing speed of more than 17,000 miles per hour (27,000 kph).

"Whenever we have a situation where we're taking on a missile more head on than from the side, that increases the challenges," O'Reilly had said.

The SBX radar is mounted on a mobile, ocean-going oil-drilling platform designed to provide the layered US missile defense system with a powerful sensor that can be positioned to cover any spot on the globe. – Reuters