U.S. State Secretary Hillary Clinton on Wednesday denied that the United States was involved in the assassination of an Iranian nuclear staff and urged Iran to end its provocative behavior, including threatening to close the Straits of Hormuz.

"I want to categorically deny any United States involvement in any kind of act of violence inside Iran," Clinton said at a press conference at the State Department alongside visiting Qatari Prime Minister and Foreign Minister Sheikh Hamad bin Jassim al-Thani.

Clinton's remarks came after a bomb attack killed an Iranian nuclear site staff and his driver in northern Tehran on Wednesday. Local reports said that the passenger being killed, identified as Mostafa Ahmadi-Roshan, was a staff member of Iran's Natanz nuclear enrichment site.

However, earlier in the day at a State Department regular briefing, spokeswoman Victoria Nuland refrained from denying the U. S. involvement in the killing.

When asked by the reporters on this issue, Nuland said "I don't have any information to share one way or the other on that."

Although she said the United States "condemn the loss of innocent life" and "condemn violence of any kind," she refused to comment on whether the killed Iranian scientist came under her definition of innocent life.

"I'm not going to speak to who may or may not have done this, one way or the other," Nuland said.

Previously, at least three Iranian nuclear scientists have been assassinated since 2010. Iran's First Vice President Mohammad-Reza Rahimi said Wednesday that Israeli agents were the perpetrators of Ahmadi-Roshan's assassination, local media reported.

Iranian Foreign Ministry spokesman Ramin Mehmanparast said Wednesday that the assassination of the country's nuclear scientist is an indication of Israel's persistence on inhumane terrorist acts, with the support of certain Western states especially the United States, to curb the "peaceful" nuclear activities of the Islamic republic, the semi-official Fars news agency reported.

At the press conference with Qatari foreign minister, Clinton also urged Iran to "end its provocative behavior, end its search for nuclear weapons, and rejoin the international community and be a productive member of it."

She also talked about the threatening by Iran to close the Straits of Hormuz, one of the world's most critical oil route, reaffirming the U.S. commitment to keep it open.

"It's part of the lifeline that keeps oil and gas moving around the world," said Clinton. "And it's also important to speak as clearly as we can to the Iranians about the dangers of this kind of provocation."

U.S., Israel accused of being behind murder

Iranian officials said Wednesday that the United States and Israel are behind the assassination of Iran's nuclear staff. Local media reported Wednesday that Mostafa Ahmadi-Roshan, a staff member of Iran's Natanz nuclear enrichment site, was killed by a car bomb attack in Gol Nabi Street near the Ketabi square in northern Tehran on Wednesday morning.

Pentagon plays down U.S.-Iran tension

U.S. Defense officials said on Wednesday that they believe tensions between the United States and Iran have cooled down recently, despite a bomb attack killed an Iranian nuclear site staff and his driver in northern Tehran on Wednesday.

Iranian nuclear scientist killed in blast
 
The death toll in Wednesday's bomb attack targeting an Iranian nuclear site staff in northern Tehran has risen to two, the official IRNA news agency reported.

Victim of Tehran bomb attack identified as "nuclear scientist"
 
A report by Iran's official IRNA news agency said Wednesday that the victim of an earlier bomb attack in Tehran was a staff of Iran's Natanz nuclear enrichment site.

Car bomb explosion kills one, injures two in Iran
 
A car bomb exploded in a square in northern Tehran Wednesday, killing one university teacher and wounding two others, local Press TV reported.