Iran denies Western allegations that it is seeking atomic weapons, insisting that it only wants to develop the peaceful use of nuclear energy.
"Our actions today are designed to deter other governments and foreign financial institutions from dealing with these entities and thereby supporting Iran's illicit activities," Timothy Geithner, the US treasury secretary, said.
"We will continue to target Iran's support for terrorist organisations ... and continue to expose Iran's efforts to evade international sanctions"
US treasury secretary
He added that more measures were planned in the coming weeks to increase financial pressure on Iran.
"We will continue to target Iran's support for terrorist organisations. We will continue to focus on Iran's Revolutionary Guard," said Geithner in announcing the move.
"And we will continue to expose Iran's efforts to evade international sanctions."
He said the US expects other countries to announce new penalties of their own against Iran soon, adding: "This is not something the United States can do alone."
The US actions come as the European Union states this week consider their own sanctions over and above the UN resolution, including actions against Iranian banks and insurance companies involved in trade finance.
The EU sanctions package is expected to be ready by mid-July.
The US treasury also identified some 20 petroleum and petrochemical companies as being under Iranian government control, a move that puts them off limits to US businesses under a general trade embargo.
The addition of Post Bank of Iran to the list of specially designated proliferators of weapons of mass destruction marks the 16th bank in Iran that the US has sought to cut off from the international financial system.
The US action also aims to thwart Islamic Republic of Iran Shipping Lines from skirting previous sanctions by renaming its vessels and shifting them to new front companies.
The treasury blacklisted five such companies, identified 27 new vessels blocked under the sanctions, and updated entries for 71 others that were renamed, reregistered and flying new flags.
The new sanctions also take further aim at Iran's Revolutionary Guard, blacklisting its air force and missile commands over their activities in the development of ballistic missiles.
The US had previously sanctioned Revolutionary Guard entities over what it says is their support for terrorist activities and Iran's nuclear and missile programmes.
Robert Einhorn, the US state department official in charge of implementing the sanctions, said the goal was to persuade Iran to return to the negotiating table.
|Ahmadinejad said Iran would make no concessions over its nuclear plans [EPA]
"We want Iran to address the legitimate concerns of the international community about its nuclear programme and its nuclear intentions."
Earlier on Wednesday Iran announced that it will build four new reactors to expand its atomic research.
Mahmoud Ahmadinejad, the Iranian president, in a televised speech vowed to force the West to "sit at the negotiating table like a polite child" before agreeing to further talks.
Iran will not make "one iota of concessions", he said, adding that he would punish world powers for the UN sanctions before announcing new conditions for negotiations.
"You showed bad temper, reneged on your promise and again resorted to devilish manners," the Iranian leader said.