US lawmakers were introducing legislation Wednesday that would tighten sanctions on Iran, even as Tehran agreed to future talks with world powers over its contested nuclear drive.

The bipartisan House bill would allow President Barack Obama to impose penalties on foreign entities that provide Iran with goods to help maintain its struggling economy.

The Nuclear Iran Prevention Act of 2013 also would provide Obama with broader authority to target strategic imports, such as mining or power generating equipment that could help Iran with its nuclear program, which the West and Israel say is a front for weapons development.

"Iran's continued march toward nuclear weapons is the gravest threat facing the United States and our allies," said bill sponsor Ed Royce, Republican chair of the House Foreign Affairs Committee.

Co-sponsor Eliot Engel, the committee's top Democrat, added that the bill aims to "tighten the screws on Iran until the regime abandons its nuclear weapons program.

"I hope this crisis can be resolved through diplomacy, but words cannot be a substitute for action, and the US must keep all options on the table," he added.

The bill would designate the Iranian Revolutionary Guard Corps as a foreign terrorist organization.

Such designations are made through the State Department, but the bill, should it pass Congress, would compel the secretary of state to determine whether the group should be placed on its list of foreign terrorist groups.

Such a listing would subject the IRGC to additional sanctions. The Revolutionary Guards are already subject to United Nations sanctions.

Similar language was inserted into Senate legislation in 2007, sparking intense debate, but the bill never became law.

The House legislation also provides for stiffer penalties for human rights violators by applying existing financial sanctions to transactions that involve such violators.

"This bipartisan legislation ramps up the pressure on Iran's regime, especially targeting those brutalizing the many Iranians demanding their human rights," Royce said.

Iran is already under the toughest sanctions regime ever devised, including four separate UN resolutions. The measures are aimed at forcing the country to rein in its nuclear program, which Tehran insists is purely peaceful.

The sanctions are biting hard, slashing oil revenue and pushing the country close to recession as it seeks ways such as bartering to stay afloat, a US Government Accountability Office report said Tuesday.

News of the proposed bill comes just as Iran concluded a key meeting in Kazakhstan with P5+1 powers -- the United States, China, Russia, Britain, France and Germany -- aimed at easing the nuclear standoff.

A revised P5+1 offer reportedly involves easing sanctions on Iran's gold and precious metals trade while simultaneously lifting some restrictions on its banking operations.

But they still want Iran to halt enriching uranium to 20 percent, which for the international community is the most worrisome part of Iran's activities.

"Things are taking a turning point and I think the Almaty meeting will be (seen as) a milestone," Iran's Foreign Minister Ali Akbar Salehi said in Vienna. The sides agreed to hold new talks in March and April.

Iran was 'interested' by nuclear talks proposal: US
Washington (AFP) Feb 27, 2013 - Iran was "interested" by updated proposals from world powers to break a stalemate over its suspect nuclear program, and must now take concrete steps to move forward, a US official said Wednesday.

Characterizing two-day talks in Kazakhstan as "useful," State Department acting deputy spokesman Patrick Ventrell said "the onus is absolutely on Iran."

But he added: "We welcome that... Iran was interested in our ideas, is going to come back to the table here, and we'd like to see them take some of the concrete steps they need to come in line with the international community's concerns."

Iran and the five permanent members of the UN Security Council -- the United States, China, Russia, Britain and France -- plus Germany, agreed Wednesday to hold new talks in March and April on the Islamic republic's disputed nuclear drive.

The latest meeting saw the leading powers, known as the P5+1, offer Iran a softening of non-oil or financial sector-related sanctions in exchange for concessions over Tehran's sensitive uranium enrichment operations.

Iran's Foreign Minister Ali Akbar Salehi, speaking in Vienna, said he was "very optimistic about the outcome" of the process.

"Things are taking a turning point and I think the Almaty meeting will be (seen as) a milestone," Salehi said.

Ventrell refused to be drawn on the details of what he called "an updated and serious proposal" to Iran to try to break the deadlock over what the West believes may be a covert bid to obtain a nuclear bomb.

He acknowledged there had been no breakthroughs in Almaty, but added that "time will tell if they're going to come back and take some of these confidence-building measures on their part so that diplomacy can continue."

The P5+1 agreed to meet again at the level of senior civil servants on March 17-18 in Istanbul, and then with chief negotiators in Almaty on April 5-6.

"It's really at the technical level where we can flesh out exactly what we expect -- they know what we expect -- but where we can flesh this out in great detail," Ventrell said.

The offer reportedly involves easing crippling sanctions on Iran's gold and precious metals trade and lifting some very small banking operations.

In return, it demands a tougher weapons inspection regime and the interruption of enrichment operations at the feared Fordo bunker facility where 20-percent enrichment goes on.