The Pentagon said a giant "bunker buster" bomb will be ready within months, adding a powerful weapon to the US arsenal amid tensions over Iran's nuclear program.

The United States has agreed to sell GBU-28 "bunker-buster" bombs to South Korea that are capable of destroying underground facilities in North Korea.

Western intelligence experts believe that Iran's nuclear facilities are so deep underground that it would be difficult for Israel to wipe them out, or even significantly damage them, with a quick airstrike.

The Pentagon is expanding its arsenal of bunker-busting bombs to knock out suspected programs to make weapons of mass destruction, such as Iran's, interviews and military planning documents show.

The U.S. has conducted the first test detonation of a massive bomb designed to crack hardened bunkers, like suspected military facilities in Iran and North Korea.

A huge mushroom cloud of dust is expected to rise over Nevada's desert in June when the Pentagon plans to detonate a gigantic 700-ton explosive -- the biggest open-air chemical blast ever at the Nevada Test Site -- as part of the research into developing weapons that can destroy deeply buried military targets.

A senior Bush administration official and the House Appropriations Committee this week declared the Energy Department’s controversial Robust Nuclear Earth Penetrator study dead. The study, intended to assess the feasibility of developing a reliable, deeper-penetrating nuclear weapon than currently in the arsenal has been the subject of domestic and international criticism. Proponents say it is needed to threaten hardened and deeply buried targets. Critics say it could cause mass civilian destruction if used, might be deemed a more “usable” weapon, and undermines global nonproliferation efforts.

Controversial plans to research nuclear “bunker busters” have been abandoned by the by the US in the country's 2006’s budget. The Pentagon will instead focus on developing a conventional deep-earth penetrating bomb.

Nuclear “bunker busters” could destroy enemy hideouts hundreds of metres underground but, if the target is in an urban area, a strike could lead to more than a million civilian deaths, warns a report from the US National Research Council (NRC)

Earth-penetrating nuclear bombs would be capable of destroying military targets deep underground, but not without inflicting "massive casualties at ground level," according to a new congressionally mandated study.