Iran has accused Israel and the United States of being behind the Wednesday morning assassination of Iranian nuclear scientist Mostafa Ahmadi Roshan.

Assassinated: Chemistry expert Mostafa Ahmadi Roshan was killed after two men on motorcycles attached magnetic bombs to his car in Tehran, Wednesday, January 11, 2012. UPDATE: According to the Inter Press Service, Iran experts say the latest assassination is likely to scuttle the already slim chances for a negotiated solution and convince the Islamic Republic that the United States and its partners are determined to overthrow the Iranian government.

"The Iranians are convinced that that is our goal," Paul Pillar, a CIA veteran and former Middle East chief on the National Intelligence Council, which advises the U.S. president, told IPS.

Pillar referred to inflammatory rhetoric by U.S. Republican presidential candidates – one of whom, former House Speaker Newt Gingrich, has explicitly called for regime change – while others apart from Texas Congressman Ron Paul have called for attacking Iran to prevent it from getting nuclear weapons.

Pillar suggested that U.S. government talking points were being influenced by domestic politics and that the Obama administration wanted to be seen as being "tough on Iran" during a year in which the president is running for re-election.

UPDATE: The US is "categorically" denying any role in today's assassination, according to ABC News:

In the face of Iranian accusations, U.S. Secretary of State Hillary Clinton said the American government is not to blame for the bombing assassination today of a man the Iranian media called a top nuclear scientist.

"I want to categorically deny any United States involvement in any kind of act of violence inside Iran," Clinton told reporters today. "We believe that there has to be an understanding between Iran, its neighbors and the international community that finds a way forward for [Iran] to end its provocative behavior, end its search for nuclear weapons and rejoin the international community and be a productive member of it."

The Associated Press is reporting:

TEHRAN, Iran (AP) — 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 another person Wednesday, state TV reported. The slayings suggest a widening covert effort to set back Iran's atomic program.

The attack in Tehran bore a strong resemblance to earlier killings of scientists working on the Iranian nuclear program. It is certain to amplify authorities' claims of clandestine operations by Western powers and their allies to halt Iran's nuclear advances. [...]

Iran has claimed that Israel's Mossad, the CIA and Britain's spy agency are engaged in an underground "terrorism" campaign against nuclear-related targets, including at least three slayings since early 2010 and the release of a malicious computer virus known at Stuxnet in 2010 that Iran says disrupted controls of some centrifuges — a key component in nuclear fuel production. Both countries have denied the Iranian accusations.

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."

Mostafa Ahmadi RoshanIran's FARS news agency described the explosion as a 'terrorist attack' targeting Mostafa Ahmadi Roshan, a 32-year old graduate of the prestigious Sharif University of Technology in Tehran.  Deputy Tehran governor Safarali Baratlou was quoted as saying: "The bomb was a magnetic one and the same as the ones previously used for the assassination of the scientists, and the work of the Zionists . Zionists seem to be trying to create a security atmosphere in Iran on the threshold of (parliamentary) elections to decrease the people' turnout in the polls." A similar bomb attack on January 12, 2010, killed Tehran University professor Masoud Ali Mohammadi, a senior physics professor.

An early Wednesday morning article in Salon titled "More Murder of Iranian Scientists: Still Terrorism?", Glenn Greenwald writes:

Does anyone doubt that some combination of the two nations completely obsessed with Iran’s nuclear program — Israel and the U.S. — are responsible? (U.S. officials deny involvement while pointing the finger at Israel, whose officials will not comment but “smile” when asked; the CIA has “targeted” Iran’s scientists in the past, several of whom have disappeared only to end up in U.S. custody, including one who “resurfaced in the United States after defecting to the CIA in return for a large sum of money”). At the very least, there has been no denunciation from any Obama officials of whoever it might be carrying out such acts.[...]

And Kevin Drum, then of Washington Monthly, went the furthest of all — in a post he entitled “Terrorism” — branding the killing of Iran’s scientists as “Terrorism”:

...After all, killing civilian scientists and civilian leaders, even if you do it quietly, is unquestionably terrorism. That’s certainly what we’d consider it if Hezbollah fighters tried to kill cabinet undersecretaries and planted bombs at the homes of Los Alamos engineers.

If you think Iran is a mortal enemy that needs to be dealt with via military force, you can certainly make that case. But if you’re going to claim that terrorism is a barbaric tactic that has to be stamped out, you can hardly endorse its use by the United States just because it’s convenient in this particular case.

In this photo provided by the International Iran Photo Agency, Iranian security forces stand guard around the site of an explosion outside a university in Tehran, Iran, Wednesday, Jan. 11, 2012. Two assailants on a motorcycle attached magnetic bombs on Wednesday to the car of an Iranian university professor working at a key nuclear facility, killing him and wounding two others, a semiofficial news agency reported. (Photo/IIPA, Sajjad Safari)