A grab taken from a video aired by the official Iranian state TV on December 18, 2011 shows one of several photos of Amir Mirza Hekmati. The 28-year-old American ex-Marine, who also holds Iranian citizenship, has been sentenced to death by an Iran judge for spying for the CIA, the Fars news agency reported on Januray 9, 2012. [Xinhua/AFP]

Amid rising tensions between the two arch-foes, White House on Monday strongly condemned Iran for giving a death sentence to alleged "CIA spy" Amir Hekmati, criticizing the Islamic republic for having a history of falsely accusing people for political reasons.

At a regular briefing, White House spokesman Jay Carney said the United States has seen the related reports and the State Department was working through the Swiss protecting powers in Tehran to confirm the veracity of those reports.

"If true, we strongly condemn such a verdict and will work with our partners to convey our condemnation to the Iranian government," he said.

The statement came after Iran's semi-official Fars news agency reported on Monday that an Iranian court had sentenced the "CIA spy" Hekmati to death.

US-Iranian Hekmati was charged with "cooperating with hostile government of the US, membership in the CIA and an attempt to accuse Iran of terrorism," said Fars.

In the court session, Hekmati confessed that he intended to penetrate Iran's intelligence systems to help the CIA and said he was deceived by the US intelligence agency, according to Fars. Fars did not say when the court had been held to hear the defendant.

On December 17, Iran's Intelligence Ministry announced that it had arrested Hekmati, a US spy, in the country. The ministry said in a statement that Hekmati is a CIA analyst tasked with infiltrating Iran's intelligence apparatus.

Carney said the espionage allegations against Hekmati were "false," adding that the Iranian regime "has a history of falsely accusing people of being spies, of eliciting forced confessions, and of holding innocent Americans for political reasons."

"We call upon the Iranian government to grant the Swiss protecting power immediate access to Mr. Hekmati, grant him access to legal counsel, and release him without delay," he said.

When asked if the Obama administration will act to intervene and protect Hekmati, Carney declined to speculate about that, saying "we take this matter very seriously and we are addressing it in the appropriate manner."

At the State Department, spokeswoman Victoria Nuland delivered the similar message, condemning the verdict "in the strongest terms" and describing the charges as "a fabrication."

She also urged the Iranian-Americans to "take particular care," citing dangers for dual Iranian-American citizens "because the Iranian government doesn't recognize dual citizenship."

The death sentence came at a time when tensions between the United States and Iran have reached a new high.

On December 31 last year, US President Barack Obama signed a bill with provisions asking for new sanctions on Iran, targeting foreign financial institutions that do business with the Islamic republic's central bank, the main conduit for its oil revenues.

According to the bill, foreign financial institutions doing business with Iran's central bank are banned from opening or maintaining correspondent operations in the US

The move, aimed at choking off Iran economically, prompted furious reactions from Iran. Recently, Iran has been holding a series of military exercises and threatened to close the Strait of Hormuz, one of the world's most critical oil route, if Western countries impose sanctions on Iran's oil exports.

On Sunday, US Defense Secretary Leon Panetta said that Washington would "not tolerate" the blocking of the Strait of Hormuz, saying that is a "red line" for the United States and "we will respond to them."