US President Barack Obama will sign on Thursday a sweeping package of tough new energy and financial sanctions on Iran over its nuclear program, the White House said.

Obama will sign the bill at 6:15 pm (2215 GMT) at the White House, his press secretary said in the daily statement Wednesday of the US president's schedule for the coming day.

The new congressional measures aim to choke off Iran's access to imports of refined petroleum products like gasoline and jet fuel and curb its access to the international banking system.

The US Senate and the House of Representatives approved the legislation -- aimed at forcing Tehran to halt its suspect nuclear program -- last week by crushing 99-0 and 408-8 margins, respectively.

The new measures, which backers described as the toughest ever unilateral US sanctions against the Islamic republic, are piled atop new UN Security Council and European sanctions.

World powers led by Washington accuse the Islamic republic of seeking to build nuclear weapons and are demanding that it freeze its uranium enrichment activity, which can be a key step towards developing an atomic arsenal.

The bill would shut US markets to firms that provide Iran with refined petroleum products that the oil-rich nation must import to meet demand because of a weak domestic refining capability.

It also takes aim at firms that invest in Iran's energy sector, including non-US companies that provide financing, insurance, or shipping services.

It could also see non-US banks doing business with certain blacklisted Iranian entities -- including Iran's elite Islamic Revolutionary Guard Corps and several banks -- shut out of the US financial system.

The bill would also enable US states and local governments to divest from foreign firms engaged in Iran's energy sector, and would tighten the existing US trade embargo on Iranian goods by curbing the number of exempted products.

Lawmakers had noted that Iran had rejected Obama's efforts, since taking office in January 2009, to engage Tehran diplomatically on issues from its nuclear program to its support for Islamist groups branded terrorists in Washington.

But they also cautioned that the bill's impact would depend on whether Obama invoked its powers rather than use his considerable authority to waive some of the most punishing measures.

The legislation also calls for the US government to identify Iranian officials who are human rights abusers and target them for sanctions like a travel ban and asset freeze.

And it would also for the first time require companies seeking US government contracts to certify that they and their subsidiaries do not do business with Iran, which denies charges it seeks nuclear weapons.

Opponents of the bill said Iran's elite would escape unscathed while its people suffered, stoking anti-US resentment rather than turning the population against leaders in Tehran.