The United States has tightened sanctions on Iran to further choke off its oil income, saying it was necessary to increase pressure on Tehran over its suspected nuclear weapons programme.
"This will significantly restrict Iran's ability to make use of the oil revenue that it's earning," a senior US official told reporters about the sanctions on Thursday.
It also set sanctions against Iranian media organisations and Tehran's Cyber Police for what it called human rights abuses for censorship.
As per the latest announcement, the Islamic Republic of Iran Broadcasting, its director, Ezzatollah Zarghami, and others are subject to sanctions that effectively block their access to the US financial system.
Iran's earnings now have to be credited to accounts in countries that buy Iranian crude.
Under the conditions, Tehran can only use the funds to buy goods from its oil customers, preventing the money from being repatriated and used on the nuclear programme the West believes is for developing weapons.
Iran says the programme is for purely civilian purposes.
Human rights groups have said Iran has used state media reports to trample dissent, and have pointed to forced confessions of political detainees in front of state media outlets.
Iran is using social media to hunt down political activists and is engaged in a campaign to filter out unwanted television
content, the senior US official said.
After Iran's 2009 presidential election, the government increased its jamming of foreign channels, including the BBC and Voice of America, the Treasury said.
The United States will target individuals and organisations in Iran "responsible for human right abuses, especially those who deny the Iranian people their basic freedoms of expression, assembly and speech," David Cohen, the undersecretary for terrorism and financial intelligence at the Treasury, said.
The Iranian Cyber Police, a unit formed in 2009 that has hacked into email accounts related to political action, deleted anti-government blogs and arrested bloggers, also comes under sanctions, the Treasury said.
The Iran Electronics Industries, which the Treasury said had helped the government crush activism by monitoring text messages, was also targeted by the sanctions.