A recent Defense Department report to Congress concludes that Iran could develop a missile capable of striking the United States by 2015. Iran already has the largest deployed ballistic missile force in the Middle East, comprising about 1,000 missiles capable of hitting targets up to 1,200 miles (1930 kilometers) away, the report warns.
The United States has 25 long-range interceptor missiles based in Alaska and California, as part of a system designed to defend the nation against an attack from North Korea or Iran.
Eight of 14 tests of the interceptors have been successful, while the remaining tests suffered software glitches and other technical problems. But U.S. officials say the system should still work in the event of an attack.
"We are confident that the system we have in place right now, the (ground-based interceptors) that are based in Alaska and California, are sufficient to protect us from such a threat coming in from Iran and North Korea," Pentagon press secretary Geoff Morrell said.
The United States is concerned increasingly about Iran's missile program, particularly because Washington believes that Tehran is moving toward building a nuclear weapon.
Michele Flournoy, a senior Pentagon policy adviser, told reporters in Singapore on Wednesday that a military strike against Iran is an option of "last resort" and "off the table in the near term" as Washington pursues economic sanctions.
Morrell said Flournoy's comments should not be interpreted as a shift in strategy.
"It clearly is not our preference to go to war with Iran, to engage militarily with Iran," he said. But "there is always the option at the president's disposal of taking military action."