LONDON – Iran has successfully developed ballistic missiles with the capability to carry nuclear warheads.

Detailed analysis of recent test firings of the Shahab-3 ballistic missile by military experts has concluded that Iran has been able to modify the nose cone to carry a basic nuclear bomb. The discovery will intensify international pressure on Tehran to provide a comprehensive breakdown of its nuclear research program.

The U.N. Security Council has given Iran 30 days to freeze its uranium enrichment program that many experts believe is part of a clandestine attempt to produce nuclear weapons.

Iran denies it is trying to acquire a nuclear arsenal. But ballistic missile experts advising America say it has succeeded in reconfiguring the Shahab-3 to carry nuclear weapons.

The Shahab-3 is a modified version of North Korea’s Nodong missile which itself is based on the old Soviet-made Scud.

The Nodong, which Iran secretly acquired from North Korea in the mid-1990s, is designed to carry a conventional warhead. But Iranian engineers have been working for several years to adapt the Shahab-3 to carry nuclear weapons.

“This is a major breakthrough for the Iranians,” a senior American official said. “They have been trying to do this for years and now they have succeeded. It is a very disturbing development.”

The Shahab 3 has a range of 800 miles, enabling it to hit a wide range of targets throughout the Middle East – including Israel.

Apart from modifying the nose cone, Iranian technicians are also trying to make a number of technical adjustments that will enable the missile to travel a greater distance.

Western intelligence officials believe that Iran is receiving assistance from teams of Russian and Chinese experts with experience of developing nuclear weapons. Experts who have studied the latest version of the Shahab have identified modifications to the nose cone. Instead of the single cone normally attached to this type of missile, the new Shahab has three cones, or a triconic, warhead. A triconic warhead allows the missile to accommodate a nuclear device and this type of warhead is normally found only in nuclear weapons.

According to the new research, the Iranian warhead is designed to carry a spherical nuclear weapon that would be detonated 2,000 feet above the ground, similar to the Hiroshima bomb. Although American defense officials believe that Iran is several years away from acquiring nuclear weapons, they point out that the warhead could hold a version of the nuclear bomb Pakistan is known to have developed. Iran has acquired a detailed breakdown of Pakistan’s nuclear weapons.