"The message is clear," Clinton said at a news conference in Washington on Monday . "If Iran's intransigence continues, it will face increasing pressure and isolation. Today, the United States is taking a series of steps to sharpen this choice."

She said President Barack Obama had signed a executive order that, “for the first time, significantly targets Iran’s petro-chemical industry…a cover for imports for sanctioned activities.”

Clinton also said the U.S. would seek to encourage other countries to impose additional sanctions against Iran.

Britain is severing its ties with Iranian banks and Canada is banning exports for the petrochemical, oil and gas industries.

The announcement comes after a report by the UN’s nuclear watchdog, the IAEA, indicated that Iran was seeking to develop a nuclear weapon.

Iran denies the claims and says its nuclear program is civilian in nature.

Iran was not referred o the UN Security Council over the report due to Russia and China’s opposition.

Russian Foreign Minister Sergei Lavrov said last week that sanctions against Iran are “exhausted” and that the dispute should be resolved through talks.

“Isolation or confrontation has no chance of success with regard to Iran,” he said.