The United States on Wednesday imposed new sanctions on Iran to choke off its oil income, saying it was necessary to increase the pressure on Tehran over its suspected nuclear weapons program.
It also set sanctions against Iranian media organizations and Tehran's Cyber Police for what it called human rights abuses for censorship.
The US Treasury said it was tightening up on countries allowed to continue buying Iranian oil without violating the US sanctions regime.
Those still permitted to buy Iranian oil will have to retain their payments outside Iran, to block Tehran's access to the funds, the Treasury said.
"So long as Iran continues to fail to address the concerns of the international community about its nuclear program, the US will impose tighter sanctions and intensify the economic pressure against the Iranian regime," said David Cohen, Treasury under secretary for terrorism and financial intelligence.
The move on oil revenues comes six months after the US said it would deny access to the US financial system to countries buying Iranian oil, with certain countries given exceptions to wind down their trade.
The new rules narrow the exceptions, the Treasury said, and require any country still buying Iranian oil to credit the payment to an account inside their own country.
"In addition to effectively 'locking up' Iranian oil revenue overseas, this provision sharply restricts Iran's use of this revenue for bilateral trade and severely limits Iran's ability to move funds across jurisdictions," the Treasury said in a statement.
The Treasury stressed that the tightening of Iran's access to foreign trade and foreign exchange would not apply to farm commodities or food, and medicine and medical devices
"Humanitarian trade with Iran is neither subject to these sanctions nor to sanctions previously imposed on Iran," the Treasury said.
The United States also placed sanctions on Islamic Republic of Iran Broadcasting, the Communications Regulatory Authority, and the Iranian Cyber Police, citing their extensive efforts to censor news and information flows as well as broadcasting forced confessions of political detainees.
"These censorship activities restrict the free flow of information in Iran and punish Iranian citizens who are attempting to exercise freedom of assembly and expression," the Treasury said.