By Ramin Mostafavi
TEHRAN, Jan 11 (Reuters) - An Iranian nuclear scientist was blown up in his car by a motorbike hitman on Wednesday, prompting Tehran to blame Israeli and U.S. agents but insist the killing would not derail a nuclear programme that has raised fears of war and threatened world oil supplies.
The fifth daylight attack on technical experts in two years, the killer's magnetic bomb delivered a targeted blast to the door of 32-year-old Mostafa Ahmadi-Roshan's silver sedan as he drove down a busy street close to Tehran University during the morning rush hour. The chemical engineer's passenger also died, Iranian media said, while a passer-by was slightly hurt.
Israel, whose military chief had warned Iran only on Tuesday to expect more mysterious mishaps, declined to comment. While many analysts saw Israeli or Western involvement as eminently plausible, the role of local or other Middle Eastern hands in a deadly shadow war of bluff and sabotage could not be ruled out.
The killing, which left debris hanging in trees and body parts on the road, came in a week of heightened tension:
Iran has started an underground uranium enrichment plant and sentenced an American to death for spying; Washington and Europe have stepped up efforts to cripple Iran's oil exports for its refusal to halt work that the West says betrays an ambition to build nuclear weapons, not the power plants Iran claims.
Iran has threatened to choke the West's supply of Gulf oil, drawing a U.S. warning that its navy was ready to open fire to prevent any blockade of the strategic Strait of Hormuz.
However, analysts saw the latest assassination, which would have taken some preparation, as part of a longer-running, cover effort to thwart Iran's nuclear development programme that has also included suspected computer viruses and mystery explosions.
While fears of war have forced up oil prices, the region has seen periods of sabre-rattling and limited bloodshed before without reaching all-out conflict. However, a willingness in Israel, which sees an imminent Iranian atom bomb as a threat to its existence, to attack Iranian nuclear sites, with or without U.S. backing, has heightened the sense that a crisis is coming.
Iran's Atomic Energy Organisation, which has failed to persuade the West that its quest for nuclear power has no hidden military goal, said the killing of Ahmadi-Roshan would not deter it: "We will continue our path without any doubt ... Our path is irreversible," it said in a statement carried on television.
"The heinous acts of America and the criminal Zionist regime will not disrupt our glorious path ... The more you kill us, the more our nation will awake."
First Vice-President Mohammad Reza Rahimi, quoted by IRNA news agency, said: "Iran's enemies should know they cannot prevent Iran's progress by carrying out such terrorist acts."
Preparing for its first national election since a disputed presidential vote in 2009 brought street protests against 30 years of clerical rule, Iran's leaders are struggling to contain internal tensions. Defiance of Israel and Western powers plays well with many voters in the nation of 76 million.
Israel, whose Mossad intelligence agency has a history of covert killings abroad, declined comment on Wednesday's bombing.
On Tuesday, armed forces chief Lieutenant-General Benny Gantz was quoted as telling members of parliament: "For Iran, 2012 is a critical year in combining the continuation of its nuclearisation, internal changes in the Iranian leadership, continuing and growing pressure from the international community and things which take place in an unnatural manner."
There was no immediate reaction to the early morning attack from the United States. Its ally Britain, whose Tehran embassy was ransacked in November, called suggestions of London's involvement "baseless" and condemned the killing of civilians.
The attack nonetheless, bore some of the hallmarks of the work of sophisticated intelligence agencies capable of circumventing Iran's own extensive security apparatus and also showing some apparent care to limit the harm to passers-by.
While witnesses spoke of a frighteningly loud explosion at 8:20 a.m. (0450 GMT) and parts of the Peugeot 405 sedan ended up in the branches of the trees lining Gol Nabi Street, much of the car was left intact. The containment of the blast to the vehicle suggested a charge designed both to be sure of killing the occupants but also to limit serious injury to those targeted.
Witnesses said a motorcycle, from which the rear pillion passenger reached out to stick the device to the side of the car, made off into the heavy commuter traffic.
Though the scientist killed -- the fourth in five such attacks since January 2010 -- was only 32, Iranian media described him as having a senior role at the uranium enrichment plant at Natanz, near Tehran. The semi-official news agency Mehr said Ahmadi-Roshan had recently met officials of the U.N. nuclear watchdog, the International Atomic Energy Agency.
IAEA officials could not confirm that, however.
Analysts say that killing individual scientists -- especially those whose lack of personal protection suggests a relatively junior role -- is unlikely to have much direct impact on Iran's nuclear programme, which Western governments allege is seeking to enrich enough uranium highly enough to let it build weapons.
Sabotage -- like mysterious reported explosions at military facilities or the Stuxnet computer virus widely suspected to have been deployed by Israel and the United States to disrupt nuclear facilities in 2010 -- may have had more direct effects.
However, assassinations may be intended to discourage Iranians with nuclear expertise from working on the programme.
Bruno Tertrais from France's Strategic Research Foundation said: "It certainly has a psychological effect on scientists working on the nuclear programme."
He cautioned, however, against assuming that Israel the United States or both were the instigators of the latest attack.
Trita Parsi, a U.S.-based expert on Iran, said the killing might, along with the heightened rhetoric of recent weeks, be part of a pattern ahead of a possible resumption of diplomatic negotiations on Iran's nuclear programme; some parties may want to improve their bargaining position, some may even see violence as a way of thwarting negotiations altogether, Parsi said.
Last month, Iran signalled a willingness to return to a negotiating process which stalled a year ago, though Western officials say a new round of talks is far from certain yet.
Iranian Foreign Ministry spokesman Ramin Mehmanparast was quoted by ISNA news agency as calling on the IAEA and other world bodies to condemn the latest killing: "If international bodies, in particular the IAEA, do not adopt a clear stance against this kind of assassination ... then they are supporting this act with their silence and should be held accountable."
The IAEA, which inspects Iranian nuclear sites including Natanz, declined to comment on the assassination, which comes ahead of an expected visit by a senior team of the Vienna-based agency to Tehran to discuss its growing concerns about suspected weapons-relevant activities in the Islamic Republic.
An IAEA official said on Monday that the team was expected in Iran "quite soon".
Iran's decision to carry out enrichment work deep underground at Fordow, near the holy city of Qom, could make it harder for U.S. or Israeli forces to carry out veiled threats to use force against Iranian nuclear facilities. The move to Fordow could narrow a time window for diplomacy to avert any attack.
The announcement on Monday that enrichment -- a necessary step to make uranium into nuclear weapons -- had begun at Fordow has given added impetus to Western efforts to impose an oil export embargo intended to pressure Tehran to negotiate a halt.
Oil prices have firmed. Brent crude is up more than 5 percent so far this year to above $113 a barrel.
The European Union on Tuesday brought forward to Jan. 23 a ministerial meeting that is likely to confirm an embargo on oil purchases. Big importers of Iranian oil are moving to secure alternative supplies away from OPEC's second biggest exporter.
Almost exactly two years ago, on Jan. 12, 2010, physics lecturer Masoud Ali Mohammadi was killed by a remote-controlled bomb attached to a motorcycle in Tehran. In November of that year, two daylight bomb attacks on the same day in Tehran killed one nuclear scientist and wounded another. A physics lecturer was shot dead in an attack in Tehran in July last year.
Despite public infighting within the Iranian establishment, Supreme Leader Ayatollah Ali Khamenei issued a clear statement on Monday that Iran had no intention of changing its nuclear course because of tightened foreign sanctions.
New U.S. sanctions have started to bite. The rial currency has lost 20 percent of its value against the dollar in the past week and Iran has threatened to shut the exit from the Gulf at the Strait of Hormuz, through which 35 percent of the world's seaborne traded oil passes.
U.S. Treasury Secretary Timothy Geithner, visiting Beijing, appealed for Chinese cooperation on nuclear non-proliferation, though Chinese officials made clear that they still opposed the U.S. sanctions and would go on buying Iranian oil.
Russia, too, came out against the U.S.-led oil embargo.
U.S. Secretary of State Hillary Clinton said Iran's move to enrich uranium near the city of Qom was "especially troubling".
"This step once again demonstrates the Iranian regime's blatant disregard for its responsibilities and that the country's growing isolation is self-inflicted," she said.
Stepping up pressure on Tehran, U.S. President Barack Obama approved a law on New Year's Eve that will sanction financial institutions dealing with Iran's central bank, a move that makes it difficult for consumers to pay for Iranian oil.
Geithner is in Asia this week to drum up support for Washington's efforts to stem the oil revenues flowing to Tehran.
After Beijing, Geithner may have an easier task in U.S. ally Japan, the next stop of his tour on Thursday, where a government source has said Tokyo will consider cutting back its Iranian oil purchases to secure a waiver from new U.S. sanctions.
Japan has already asked OPEC producers Saudi Arabia and the United Arab Emirates to supply it with more oil. South Korea is also considering alternative supplies. (Additional reporting by Parisa Hafezi and Mitra Amiri in Tehran, Allyn Fisher-Ilan in Israel, Fredrik Dahl in Vienna, Lucy Hornby in Beijing and Andrew Quinn in Washington; Writing by Parisa Hafezi and Alastair Macdonald,; Editing by Peter Millership)