The United States took steps Wednesday to tighten economic sanctions on Iran, seeking to set up additional hurdles to that nation's collection of needed oil revenues.

The actions will cut even further the money that Iran can bring in from countries it still sells crude oil to.

Some of these countries have been participating in the sanctions under the "significant reductions" clause of U.S. sanctions laws, meaning that they had made significant reductions in the amount of oil they were buying from Iran.

Countries including China, Japan, South Korea and India have reduced purchases enough to satisfy the U.S. laws and not be subject to bank sanctions themselves.

"Tightening the screws" is the way one senior administration official described the new rules. If the value of the oil Iran sells to a country exceeds the value of goods that country sells to Iran, the excess revenue will be put in a special bank account. Before Iran can access that money, it will have to find more products it can purchase from the country.

Most of the world's oil trade is done in dollars, and the new sanctions essentially turn the trade with these countries into a barter arrangement, keeping dollar-denominated accounts out of Iran's control.

Limiting Iran's ability to repatriate oil revenue, along with other sanctions, will "continue to intensify until Iran agrees to cooperate with Western demands over its ongoing uranium enrichment and presumed nuclear weapons program," said a second senior administration official, speaking during a conference call with reporters.

This official added that the United States had consulted the countries covered under this new rule and had received no objection.

The Treasury Department announced the actions 180 days after President Barack Obama signed the Iran Threat Reduction and Syria Human Rights Act of 2012, which expanded the United States' sanctions power against Tehran.

The sanctions are aimed at bringing Iran to the negotiating table over its disputed nuclear program. Iran has said its nuclear intentions are peaceful.

The United States also is cracking down on Tehran's restrictions on its own citizens by placing Islamic Republic of Iran Broadcasting on the sanctions list.

A Treasury Department statement noted complaints by human rights groups that state-media transmissions are being used to trample dissent.

They point to "distorted or false IRIB news reports and the broadcasting of forced confessions of political detainees, such as one involving Newsweek journalist Maziar Bahari, who was forced to give a false confession in front of state media outlets while jailed in 2009."

Also named in the statement is the Iranian Cyber Police unit. U.S. officials say the Cyber Police have been filtering websites, monitoring Internet behavior, and hacking e-mail accounts related to political action on the Internet, most of which has been acknowledged by the Iranian government itself in threatening announcements to the Iranian public.

The Treasury Department notes that in December 2011, the Iranian Cyber Police arrested blogger Sattar Beheshti, reportedly for anti-government comments he posted online. Beheshti, who was kept in detention without a warrant, died in custody in early November, allegedly during interrogation.

U.S. State Department spokeswoman Victoria Nuland on Wednesday said the sanctions are "about providing the opportunity for a different course if Iran decides to take it."

"Our hope is that after applying the toughest sanctions we've had in international history and continuing to be unified as an international community, that this round will offer a real opportunity for Iran to discuss substance," Nuland told reporters.