Iranian President's Office, File) NO SALES, Associated Press
FILE - In this April 8, 2008 file photo provided by the Iranian President's Office, Iranian President Mahmoud Ahmadinejad, center, visits the Natanz Uranium Enrichment Facility some 200 miles (322 kilometers) south of the capital Tehran. Iran has begun uranium enrichment at a new underground site well protected from possible airstrikes, a leading hardline newspaper reported Sunday, Jan. 8, 2011.

TEHRAN, Iran — Two assailants on a motorcycle attached magnetic bombs to the car of an Iranian university professor working at a key nuclear facility, killing him and wounding two people on Wednesday, a semiofficial news agency reported.

The attack in Tehran bore a strong resemblance to earlier killings of scientists working on the Iranian nuclear program. It is certain to reinforce authorities' claims of widening clandestine operations by Western powers and allies to try to cripple nuclear advancements.

The bomb killed Mostafa Ahmadi Roshan, a chemistry expert and a director of the Natanz uranium enrichment facility in central Iran, the semiofficial Fars news agency reported. Natanz is Iran's main enrichment site, but officials claimed earlier this week that they are expanding some operations to an underground site south of Tehran with more advanced equipment.

The U.S. and its allies are pressuring Iran to halt uranium enrichment, a key element of the nuclear program that the West suspects is aimed at producing atomic weapons. Uranium enriched to low levels can be used as nuclear fuel but at higher levels, it can be used as material for a nuclear warhead. Iran denies it is trying to make nuclear weapons.

The killing of Roshan was similar to previous assassinations of Iranian nuclear scientists that Tehran has blamed on Israel's Mossad and the United States. Both countries have denied the accusations.

But Israeli officials have hinted about covert campaigns against Iran without directly admitting involvement.

On Tuesday, Israeli military chief Lt. Gen Benny Gantz was quoted as telling a parliamentary panel that 2012 would be a "critical year" for Iran — in part because of "things that happen to it unnaturally."

Safar Ali Baratloo, a senior security official, was quoted by Fars as saying the attack was the work of Israelis.

"The magnetic bomb is of the same types already used to assassinate our scientists," he said. "The terrorist attack is a conspiracy to undermine the (March 2) parliamentary elections."

Roshan, 32, was inside the Iranian-assembled Peugeot 405 car together with two others when the bomb exploded near Gol Nabi Street in north Tehran, Fars reported.

Fars described the explosion as a "terrorist attack" targeting Roshan, a graduate of the prestigious Sharif University of Technology in Tehran.

Roshan was a chemistry expert who was involved in building polymeric layers for gas separation, which is the use of various membranes to isolate gases. He was also deputy director of Natanz uranium enrichment plant, in central Iran, for commercial affairs. According to conservative news website, mashreghnews.ir, Roshan was in charge of purchasing and supplying equipment for Natanz enrichment facility.

A similar bomb explosion on Jan. 12, 2010, killed Tehran University professor Masoud Ali Mohammadi, a senior physics professor. He was killed when a bomb-rigged motorcycle exploded near his car as he was about to leave for work.

In November 2010, a pair of back-to-back bomb attacks in different parts of the capital killed one nuclear scientist and wounded another.

The slain scientist, Majid Shahriari, was a member of the nuclear engineering faculty at Shahid Beheshti University in Tehran and cooperated with the Atomic Energy Organization of Iran. The wounded scientist, Fereidoun Abbasi, was almost immediately appointed head of Iran's atomic agency.

And in July 2011, motorcycle-riding gunmen killed Darioush Rezaeinejad, an electronics student. Other reports identified him as a scientist involved in suspected Iranian attempts to make nuclear weapons.

Rezaeinejad allegedly participated in developing high-voltage switches, a key component in setting off the explosions needed to trigger a nuclear warhead.

The United States and other countries say Iran is trying to develop nuclear weapons technology. Iran denies the allegations, saying that its program is intended for peaceful purposes.

The latest blast is certain to bring fresh charges by Iran that the U.S. and allies are waging a clandestine campaign of bloodshed and sabotage in attempts to set back Iran's nuclear efforts.

"Instead of actually fighting a conventional war, Western powers and their allies appear to be relying on covert war tactics to try to delay and degrade Iran's nuclear advancement," said Theodore Karasik, a security expert at the Dubai-based Institute for Near East and Gulf Military Analysis.

He said the use of magnetic bombs bears the hallmarks of covert operations.

"It's a very common way to eliminate someone," he added. "It's clean, easy and efficient."

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Associated Press writer Brian Murphy in Dubai, United Arab Emirates, and Amy Teibel in Jerusalem contributed to this report.