Iran said one of its nuclear scientists was killed on Wednesday by a magnet bomb fixed to his car by a motorcyclist. Tehran blamed Israel for the attack, intensifying diplomatic tensions in the West over Tehran's nuclear programme.
The bombing, which Iranian officials said bore all the hallmarks of assassinations of other nuclear scientists in past years, came as Washington sought to persuade a sceptical China to help efforts to toughen sanctions against Iran.
Iran has blamed Israeli, British and US intelligence for past attacks, which it said were aimed at assassinating key people working on Iran's nuclear programme. Both Israel and the United States have rejected the claims.
"The bomb was a magnetic one – the same as ones previously used for the assassination of the scientists, and is the work of the Zionists," Tehran Deputy Governor Safarali Baratlou told the semi-official Fars news agency, referring to Israel.
"Iran's enemies should know they cannot prevent Iran's progress by carrying out such terrorist acts," state news agency IRNA quoted First Vice-President Mohammad Reza Rahimi as saying.
Heightened tensions over the nuclear programme, which major oil producer Iran insists is purely for civilian use but Western powers suspect has military applications, have driven oil prices higher, with Brent crude up more than 5 per cent since the start of the year to above $113 a barrel.
The European Union has brought forward to 23 January a ministerial meeting that is likely to confirm an embargo on oil purchases, and big importers of Iranian oil are moving to secure alternative supplies.
Iran is the Organization of the Petroleum Exporting Countries (OPEC)’s second biggest exporter.
The victim was a nuclear scientist who "supervised a department at the Natanz uranium enrichment facility," Fars said.
Iran's Atomic Energy Organisation confirmed in a statement that chemistry engineer Mostafa Ahmadi-Roshan had been part of Iran's nuclear enrichment programme and vowed not to be deterred from its development of nuclear technology.
"America’s and Israel's heinous act will not change the course of the Iranian nation," it said.
Witnesses told Reuters they had seen two people on the motorcycle fix the bomb to the car. As well as the person killed in the car, a pedestrian was also killed. Another person in the car was gravely injured, they said.
Other Iranian media also reported the death but there were differing accounts of the killing.
Two daylight bomb attacks on the same day in Tehran in November 2010 killed one nuclear scientist and wounded another. Physics lecturer Masoud Ali Mohammadi was killed in January 2010, when a remote-controlled bomb attached to a motorcycle exploded near his car in Tehran.
There was no immediate claim of responsibility for Wednesday's attack.
"It is not our practice to comment on this sort of speculation," an Israeli official, when asked about Tehran's accusation over Wednesday's killing.
On Tuesday, Israel's military chief of staff, Lieutenant-General Benny Gantz, was quoted as saying that Iran should expect more "unnatural" events in 2012.
His comments, made before a closed-door parliamentary panel in Jerusalem, were widely interpreted as alluding to previous acts of sabotage.
"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," Gantz was quoted as saying.
"It's impossible to say who is behind the apparently carefully targeted attacks on Iranian nuclear scientists over the past couple of years. But Iranian perceptions will be that Israel, the US and other Western states are behind the attacks, seeking as they are to sabotage the Iranian nuclear programme," said Gala Riani at IHS Global Insight.
"It's hard to say whether it (Wednesday's attack) could be in response to anything really. If it is being carried out by foreign intelligence services then it’s more likely to be part of a longer-term agenda to derail and set back Iran's nuclear programme ... rather than a quick-reaction to the start of enrichment activities," Riani added.
Stepping up pressure on Tehran, US 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.
Nuclear talks between Iran and the five permanent UN Security Council members plus Germany collapsed one year ago over Iran's refusal to negotiate over its right to enrich uranium.
The United States and Israel say they are leaving the military option on the table in case it becomes the only way to prevent Iran from making a nuclear weapon.