WASHINGTON (Reuters) - Iran may be able to build a missile capable of striking the United States by 2015, according to an unclassified Defense Department report on Iran’s military sent to Congress and released on Monday.

“With sufficient foreign assistance, Iran could probably develop and test an intercontinental ballistic missile (ICBM) capable of reaching the United States by 2015,” said the April report, a copy of which was obtained by Reuters.

A classified version was also submitted to Congress.

The timing of advances in Iran’s long-range missile technology is being closely watched in Washington, which accuses Tehran of pursuing nuclear weapons and is pushing for a new round of sanctions. Iran denies the charges and says its nuclear program is for peaceful purposes.

“Iran’s nuclear program and its willingness to keep open the possibility of developing nuclear weapons is a central part of its deterrent strategy,” the report said.

The U.S. military tried and failed to shoot down a simulated Iranian missile strike on the United States in January, in a botched $150 million exercise over the Pacific Ocean. That attempt failed because of a malfunction in a radar built by Raytheon Co.

It was not immediately clear whether the latest estimate on Iran’s missile technology was a departure from a May 2009 National Intelligence Estimate, which deemed Tehran unlikely to have a long-range missile until between 2015 and 2020, according to U.S. officials who saw the report at the time.

The 2009 estimate was revised from an earlier range of between 2012 to 2015.

Representative Ike Skelton, chairman of the House of Representatives Armed Services Committee, called the report a “comprehensive view of the military situation in Iran.”

LEBANON RE-ARMED, TALIBAN SUPPORT

The report also included an assessment of Iran’s broader military capabilities and support for insurgents in Iraq and Afghanistan, as well as groups like Hamas in the Palestinian territories and Hezbollah in Lebanon.

With Iranian support, Hezbollah has replenished its arsenal beyond levels it had in the 2006 war with Israel, the report said, without offering specifics.

“Iran, through its long-standing relationship with Lebanese (Hezbollah), maintains a capability to strike Israel directly and threatens Israeli and U.S. interests worldwide,” it said.

The report cited recently uncovered caches of weapons that Iran’s Qods Force gave to Afghan militants. They contained “large amounts of Iranian-manufactured weapons,” including 107 mm rockets.

It estimated the size of Iran’s “Ground Force” at 220,000 personnel and the Revolutionary Guard Corps’s “Ground Resistance Forces” at 130,000 personnel. It said Iran had between 1,800 and 1,900 tanks.

President Barack Obama’s national security advisers are considering a broad range of options to curb Iran’s nuclear program, among them military strikes, if diplomacy and sanctions fail.

Admiral Mike Mullen, chairman of the U.S. military’s Joint Chiefs of Staff, said on Sunday the military options available to Obama would go “a long way” to delaying Iran’s nuclear progress but may not set the country back long-term.

He called a military strike his “last option” right now and has repeatedly warned of potential, unintended consequences of any action against Iran.