President Barack Obama said Thursday he had extended one of the many levels of sanctions against Iran, imposed in 1995 over claims Tehran dealt in terrorism and sought weapons of mass destruction.

The sanctions, prohibiting US companies aiding the development of the Iranian oil industry and halting trade, export/import and investment ties with Iran, were imposed by the Clinton administration and have been extended on an annual basis by successive presidents.

They would have expired without Obama''s formal action to extend them.

"The actions and policies of the Government of Iran are contrary to the interests of the United States in the region and pose a continuing unusual and extraordinary threat" to US national security and the US economy, Obama said in a message to Congress.

The sanctions are one portion of the large range of punitive US, United Nations and international measures imposed against Iran, for various reasons, including its alleged backing for terrorism and nuclear drive.

Over more than 20 years, Washington has steadily upped sanctions against Iranian entities in hopes of pressuring Tehran to pull back on its nuclear program -- which the US says is aimed at developing nuclear weapons.

The United States says Iran must also halt its alleged support for groups Washington has labelled "terrorist," including Lebanon''s Hezbollah and armed Palestinian groups.