A group of US lawmakers Wednesday unveiled legislation to toughen sanctions on Iran for its nuclear energy program, calling for international companies traded on US exchanges to reveal investments in the Islamic Republic.

"If we can bring greater transparency to any investment being made in Iran, we can defund the nuclear militarization of one of the world's most hostile nations," said Senator Kirsten Gillibrand, a New York Democrat who is one of the sponsors of the bill.

"Companies must make a choice: do business with Iran, or have access to the US economy... We have to have a zero tolerance policy for any company that puts profit ahead our safety or the safety of our allies."

The legislation was co-sponsored by Republican Senator Mark Kirk of Illinois, and in the House of Representatives by Ted Deutch, a Florida Democrat, and Dan Burton, a Republican from Indiana.

The bill would tighten sanctions already in place by Washington and the United Nations on Iran, which is suspected of using its nuclear program for illicit atomic weapons.

The lawmakers said the bill would require companies to disclose any sanctionable investments in Iran in their quarterly and annual reports to the Securities and Exchange Commission, and require US banks to report activities in Iran by their foreign correspondent banks.

Gillibrand said there are eight companies with affiliates quoted on the New York Stock exchange or Nasdaq that support Iran's energy sector, in addition to 18 banks.

"Congress must do more to expose companies that violate our laws and undermine our sanctions policies," Kirk said. "This bipartisan legislation would hold bad actors accountable for subsidizing a dangerous and hostile regime."

The lawmakers cited a recent report from the Foundation for Defense of Democracies that indicated eight global firms linked to Iran's energy program: Alcatel-Lucent of France, China National Offshore Oil Company, China National Petroleum Company, China Petroleum & Chemical Corp, Japan's Mitsubishi and Mitsui, Anglo-Dutch firm Royal Dutch Shell, and Sasol of South Africa.

The think tank also said 18 banks conduct business with Iran through foreign correspondent banking relationships, including large US banks and financial firms from Japan, Britain, Germany, Switzerland, France and India.