Originally posted by the Voice of America. Voice of America content is produced by the Voice of America, a United States federal government-sponsored entity, and is in the public domain. January 23, 2012 Covert War on Iran Heats Up Gary Thomas EU foreign policy chief Catherine Ashton holds a news conference at the end of a European Union foreign ministers meeting in Brussels, January 23, 2012. Photo: Reuters EU foreign policy chief Catherine Ashton holds a news conference at the end of a European Union foreign ministers meeting in Brussels, January 23, 2012. Western pressure on Iran over its nuclear program continues to mount. The European Union agreed Monday to impose an embargo on Iranian oil and freeze assets of the central bank. Iranian officials restated their threat to block the strategic Strait of Hormuz, through which one-fifth of world oil supplies flow, in retaliation. Iran is also feeling pressure from a heightened campaign of covert action. Covert warfare A string of killings of people associated with Iran's nuclear program, a series of unexplained explosions at Iranian military facilities, and introduction of a deadly computer virus are signs, analysts say, that the campaign of covert warfare against Iran has been ratcheted up. Undated photo released by Iranian Fars News Agency, claims to show Mostafa Ahmadi Roshan, who they say was killed in a bomb blast in Tehran, Iran, January 11, 2012. AP Undated photo released by Iranian Fars News Agency, claims to show Mostafa Ahmadi Roshan, who they say was killed in a bomb blast in Tehran, Iran, January 11, 2012. In the most recent case, Iranian nuclear scientist Mostafa Ahmadi Roshan was killed Jan. 11 by a magnetic bomb attached to his car. Reva Bhalla, Middle East analyst with the private intelligence firm Stratfor, says policymakers turn to covert action as a course between diplomacy and warfare. "That's when policymakers turn to that grey area of covert operations as a means to deal with the situation when you lack better options," said Bhalla. "And so the covert campaign is something that has been in the making for years now, and we're seeing an intensification of it precisely because all of the United States and its allies are increasingly concerned with Iran's rising and are looking for ways to limit it." Three other Iranian nuclear scientists have been killed over the past two years. No one has publicly claimed responsibility for the deaths. But Iran has blamed the intelligence agencies of the United States, Britain, and Israel. The United States categorically denied any involvement and Britain did not comment. Israeli officials denied knowing who was involved in the killing, but one Israeli spokesman said he was not, as he put it, shedding tears about it. Covert action is intended to influence events with a hidden hand. Desperate measures Usually carried out by a nation's intelligence agencies, operations can range from trying to swing a foreign election to sabotage and assassination. But such are risky because of the possibility of public exposure. Will Tobey, a senior fellow at Harvard University's Belfer Center for Science and International Affairs, says whoever is carrying out the killings is willing take the risk. "Well, I would say that anybody who was undertaking an assassination campaign against Iran had clearly reached a conclusion that matters were very serious and they were down to desperate measures," said Tobey. "That may point to increased danger in the near future." Michael Eisenstadt, director of the military and security studies program at The Washington Institute for Near East Policy, says Israel fits that description. He says Israel seeks to slow down Iran's nuclear progress, even if it can't stop it short of using military force. "I don't think that the Israelis look at covert action to halt Iran's nuclear program," he said. "It didn't work with the Iraqi program. And I think their experience with targeted killings has taught them that targeted killings don't halt terrorism as well. But I think they seek incremental advantage by engaging in covert operations to buy time for sanctions to work because sanctions by their very nature are slow-acting." Few analysts believe the covert action will deter Iran's leaders from their nuclear ambitions. Iran's games Iranian-American Amir Mirza Hekmati, sentenced to death by Iran's Revolutionary Court on charge of spying for the CIA, speaks during a recorded interview in an undisclosed location, in this undated still image taken from video by Reuters TV, Jan. 9, 2012. Reuters Iranian-American Amir Mirza Hekmati, who has been sentenced to death by Iran's Revolutionary Court on the charge of spying for the CIA, speaks during a recorded interview in an undisclosed location, in this undated still image taken from video by Reuters TV, January 9, 2012. But Iran has been engaging in its own spy games. Late last year, the U.S. announced an Iranian plot had been uncovered to assassinate the Saudi ambassador to Washington, but many of the details are murky. Iran has periodically arrested visitors and charged them with espionage, often to use them as bargaining chips. Earlier this month, Amir Hekmati, a former U.S. Marine was sentenced to death by an Iranian court on espionage charges. His family and the U.S. government have denied the spying allegations.