But citing unnamed U.S. officials, the newspaper said the military was stepping up efforts to make it more powerful.
The 13.6-ton “bunker-buster” bomb, known as the Massive Ordnance Penetrator, was specifically designed to take out the hardened fortifications built by Iran and North Korea, the report said.
In a report issued in November, the International Atomic Energy Agency said intelligence from more than 10 countries and its own sources “indicates that Iran has carried out activities relevant to the development of a nuclear device.”
It detailed 12 suspicious areas such as testing explosives in a steel container at a military base and studies on Shahab-3 ballistic missile warheads that the IAEA said were “highly relevant to a nuclear weapon program.”
Iran, which has come under unprecedented international pressure since the publication of the report, with Washington and the EU targeting its oil sector and central bank, rejected the dossier as based on forgeries.
Amid forecasts Iran might be able to build a bomb next year, and with President Barack Obama facing re-election campaign questions on how he can make good on promises - to Americans and to Israel - not to tolerate a nuclear-armed Islamic Republic, a decade of dispute risks accelerating towards the brink of war.
Western diplomats see little immediate prospect of renewed talks between Iran and the U.N.’s International Atomic Energy Agency, scheduled from Sunday to Tuesday in Tehran, as likely to elicit much in the way of concessions to Western demands.
For all the tension, there was little clear market response to Friday’s talk by members of Iran’s parliament that they may vote on Sunday to stop sending oil to the European Union - its second biggest customer - as early as next week, to spite EU states that gave themselves until July to enforce an oil import embargo on Iran.
Meanwhile, doubts about its bomb’s effectiveness prompted the Pentagon this month to secretly submit a request to Congress for funding to enhance the bomb’s ability to penetrate deeper into rock, concrete and steel before exploding, The Journal noted.
The Defense Department has spent about $330 million so far to develop about 20 of the bombs, which are built by Boeing Co., the report pointed out.
The Pentagon is seeking about $82 million more to make the bomb more effective, The Journal said.
Defense Secretary Leon Panetta, in an interview with The Journal Thursday, acknowledged the bomb’s shortcomings against some of Iran’s deepest bunkers.
He said more development work would be done and that he expected the bomb to be ready to take on the deepest bunkers soon.
“We’re still trying to develop them,” Panetta said.
Citing unspecified procurement documents, the newspaper said the Navy is converting an aging warship it had planned to decommission into a makeshift staging base for the commandos in response to requests from the U.S. Central Command.
Unofficially dubbed a “mothership,” the floating base could accommodate smaller high-speed boats and helicopters commonly used by Navy SEALs, the report said.
Special operations forces are a key part of President Barack Obama’s strategy to make the military leaner and more agile as the Pentagon confronts at least $487 billion in spending cuts over the next decade, the paper noted.
Mike Kafka, a spokesman for the Navy’s Fleet Forces Command, declined to elaborate on the floating base’s purpose or to say where, exactly, it will be deployed in the Middle East, The Post said.
Other Navy officials acknowledged that they were moving with unusual haste to complete the conversion and send the mothership to the region by early summer, the report said.
Navy documents indicate that it could be headed to the Persian Gulf, where Iran has threatened to block the Strait of Hormuz, The Post noted.