|The Iranian nuclear scientist was killed by a bomb placed on his car by a motorcyclist in Tehran [Reuters]
US officials have denied any role in the apparent killing of an Iranian nuclear scientist, and condemned the bomb attack which Tehran said was linked to Washington and Israel.
"I want to categorically deny any United States involvement in any kind of act of violence inside Iran," Hillary Clinton, the US Secretary of State, told reporters on Wednesday when asked about Iranian allegations over the attack.
Tommy Vietor, a National Security Council spokesman, added: "The United States had absolutely nothing to do with this. We strongly condemn all acts of violence, including acts of violence like this."
Victoria Nuland, Clinton's spokeswoman, said the state department condemned "any assassination or attack on an innocent person and we express our sympathies to the family".
This comes following the death of Mostafa Ahmadi Roshan, a nuclear scientist who supervised a department at the Natanz uranium enrichment facility. He was killed on Wednesday in an explosion outside a university campus in Tehran.
In a letter, Iran's government demanded the UN Security Council strongly denounce the killing.
Mohammad Khazaee, Iran's UN ambassador, called on UN Secretary General Ban Ki-moon, the 15-nation Security Council and UN General Assembly president Nassir Abdulaziz al-Nasser to condemn the killings "in the strongest terms".
"There is firm evidence that certain foreign quarters are behind such assassinations," Khazaee said.
The country's powerful Revolutionary Guards were also adamant that "the terrorist actions against our nuclear scientists and experts is a US-Zionist plot," the AFP news agency reported.
War of words
Wednesday's attack has deepened a war of words between Washington and Tehran already raging over Iranian nuclear ambitions and maritime tensions.
Iranian officials noted that the manner of the attack on Roshan - two men on a motorbike attaching a magnetic bomb to the target's vehicle - bore similarities to the killings of three other scientists over the past two years.
At least two of those scientists had also been working on nuclear activities. Those attacks were viewed by Iranian officials as assassination operations carried out by Israel's Mossad intelligence service, possibly with US assistance.
Mohammad Reza Rahimi, Iran's vice president, on Wednesday blamed Israeli agents for the attack, but said they could not "prevent progress'' in what Iran claims are peaceful nuclear efforts.
He said the killing was "evidence of [foreign] government-sponsored terrorism" but vowed it would not stop Iran's nuclear programme.
"Today those who claim to be combating terrorism have targeted Iranian scientists," he said. "They should know that Iranian scientists are more determined than ever in striding towards Iran's progress."
The US and Israel say Iran is trying to develop nuclear weapons technology. Iran denies the allegations, saying that its programme is intended for peaceful purposes.
In Israel, a senior official said he was unaware who carried out Wednesday's attack which he called an act of "revenge".
"I don't know who took revenge on the Iranian scientist, but I am definitely not shedding a tear," Brigadier General Yoav Mordechai, a military spokesman, wrote on his official Facebook page.
Aircraft carrier deployed
The increased tension over the attack comes as a second US aircraft carrier, the USS Carl Vinson, arrived in the Gulf region, the Pentagon said on Wednesday, in a move it called "routine".
The Carl Vinson was due to relieve another aircraft carrier, the USS John Stennis, which is in the region, Pentagon spokesman John Kirby told reporters.
"Her deployment in that area is routine, long-planned - there's nothing unusual about that," Kirby explained.
Despite the Pentagon's denials of a build-up in the region, the USS Abraham Lincoln was in the Indian Ocean and en route to join the Carl Vinson, according to the US Navy.
"The fact that there are two carriers in that AOR [area of responsibility] is not an indication of anything specific in respect to Iran," the spokesman stressed, insisting: "There is no change to force posture in the region."
The military buildup comes with the US steadily ratcheting up sanctions on Iran with the aim of fracturing its oil-dependent economy in a bid to halt its nuclear programme.
Iran has responded by saying it could close the Strait of Hormuz, the gateway to the Gulf, potentially blocking the maritime flow of 20 per cent of the world's oil if it is attacked or if sanctions halt its petroleum exports.