Crews load the massive ordnance penetrator in a test in 2007 at White Sands Missile Range in southern New Mexico. The conventional bomb is designed to defeat deeply buried targets such as bunker and tunnel facilities. (Defense Threat Reduction Agency/Associated Press)

The Pentagon is speeding up the deployment of an enormous bomb designed to destroy hidden weapons bunkers buried deep underground, one that would be the largest non-nuclear weapon in the U.S. arsenal.

The 13.6-tonne massive ordnance penetrator (MOP) carries about 2,400 kilograms of explosives and is so heavy only one can be carried aboard a B-2 Stealth bomber.

The U.S. Department of Defence's decision to award the $51.9 million US contract to Boeing Co. earlier this month signals a renewed commitment to the weapon, which began testing in 2007 but had languished for two years because of budgetary issues. It is being designed jointly by Boeing and defence contractor Northrop Grumman.

The decision to provide further funding suggests the Obama administration is considering the weapon as part of a long-range backup plan if diplomatic efforts fail with countries believed to be pursuing nuclear weapons programs.

The U.S. is currently engaging in multilateral talks with both North Korea and Iran over the respective nuclear programs of the two countries. North Korea is a known nuclear weapons state and has exploded working devices underground, while Iran recently revealed a nuclear site deep inside a mountain near the holy city of Qom, though it says the facility is for energy purposes only.

Rhetoric toned down

The Obama administration has been careful not to take military action off the table against Iran, but has tried to distance itself from the tougher rhetoric that characterized the previous administration of George W. Bush.

Joint Chiefs of Staff chairman Adm. Mike Mullen, for example, has said a strike is an option he doesn't want to use.

Pentagon officials acknowledge the new bomb is intended to blow up fortified sites such as those used in Iran and North Korea, but denied they had any targets in mind.

"I don't think anybody can divine potential targets," Pentagon press secretary Geoff Morrell said. "This is just a capability that we think is necessary given the world we live in."

Kenneth Katzman, a specialist on Iran and the Middle East at the Congressional Research Service, said the weapon may act as a deterrent down the road.

"It adds to the calculus, let's say, of [Iranian President Mahmoud] Ahmadinejad and [North Korean leader] Kim Jong Il," Katzman said.

The precision-guided MOP bomb is designed to drill through earth and reinforced concrete before exploding. The bomb is about 10 times more powerful than the U.S. Massive Ordnance Air Blast — nicknamed the Mother Of All Bombs — the weapon it is designed to replace.

With files from the Associated Press