Tactical nuclear weapons would be required to penetrate the defenses Iran has constructed around its nuclear facilities, according to Col. (res.) Shlomo Mofaz, an international consultant on terrorism and intelligence and a research fellow at the Institute of Counterterrorism at the Interdisciplinary Center in Herzliya.

Mofaz argued that any preemptive action - not necessarily launched by Israel - against Iran's nuclear facilities would need to employ tactical nuclear weapons.

"The Iranians have invested a lot of money to hide their weapons and infrastructure underground. The most sensitive items are below the surface," he said.

"American experts have said they are not sure that conventional weapons would be able to infiltrate these sites," he said. "Based on information from public sources, any attack should use tactical nuclear weapons."

As reported in Time magazine on Monday, a recent Pentagon report outlining US military options to the Iranian threat mentions the difficulty of locating all targets. It also states that Iran's reinforced facilities constitute a strategic challenge to any military action. The report suggests that repeated air strikes using laser and satellite guided missiles would be necessary.

Mofaz added that the Iranians have studied US and Israeli techniques for destroying infrastructure and weapons stores, and therefore have built these bunkers as a response.

As the UN Security Council begins the process of bringing potential sanctions against Iran to a vote, Mofaz stressed that the Iranian strategy in relation to the UN was one of foot-dragging, an attempt to buy time while the nuclear drive advances.

"The Iranian administration is gaining more time to push forward to finish its program," said Mofaz, adding that the sanction moves had come too late.

According to Mofaz, there are two essential aspects to an Israeli response to the threat from Iran: The need to deploy the Arrow antimissile system - which would be effective only if Teheran were to employ a small number of missiles, but not against larger volleys - and to develop a second-strike capability.

"Second-strike capabilities are based on the assumption that Israel has nuclear weapons," he noted, "something which has not been confirmed by the Israeli government."

Regarding a preemptive strike against Iranian nuclear facilities, Mofaz said that according to the principles of the IDF, as first set out by David Ben-Gurion, "Israel must have full capability to defend itself; there must be a program and plan to deal with the Iranian threat... The IDF needs to have the capability to eliminate this threat."

Mofaz warned, however, that both the appropriate timing for such a strike and whether the IDF was capable of destroying Iran's nuclear program were unknown.

"The difficulty of such a strike stems from the possibility that there are many unidentified nuclear development sites and the limited usefulness of conventional air strikes against nuclear facilities," he said.