Obama Signs Order Blocking All Iranian Assets in U.S.

U.S. President Barack Obama on Monday ordered new sanctions into force on Iran, including its central bank, seeking to tighten a choke hold on Tehran's economy as a nuclear showdown deepens.

Obama signed an executive order implementing parts of a new sanctions regime passed by Congress late last year at a time of high tensions with Iran and rampant speculation about a possible Israeli strike against its nuclear sites.

The measures block all property and interests of the Iranian government, the Central Bank of Iran (CBI) and all Iranian financial institutions that come within U.S. jurisdiction.

Previously, U.S. institutions were required to reject, rather than block, such Iranian transactions.

The measures, passed with wide majorities in Congress last year, also included a requirement for Obama to impose sanctions on foreign financial institutions that do business with the CBI or other Iranian finance firms.

That move was designed to strangle Iran's access to foreign finance and commerce and to cripple its lucrative oil and energy industry by effectively barring foreign firms that do business with Tehran from the U.S. financial system.

Obama's action on Monday however does not implement those sanctions, but the Treasury Department warned that firms doing business with Iran "remain at risk" of U.S. punishments.

The president has the power to issue waivers to halt the impact of such sanctions, once they come into force, every 120 days.

Senior White House officials are currently studying the measures passed by Congress to find a way to implement them that maximizes pain for Iran, but does not cause a huge spike in oil prices, for instance, that could harm the fragile U.S. economic recovery.