Tensions between the United States and Iran have reached a new high recently.

On Dec. 31 last year, 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 U.S.

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, U.S. 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."

In the latest development, Iran had sentenced the alleged "CIA spy" Amir Hekmati, who has a dual Iranian-American citizenship, to death, which has drawn strong condemnation from the Untied States.