The United States on Thursday placed additional sanctions on what it called Iran's nuclear proliferation network.
The Treasury Department said 11 companies and four individuals were being from barred doing business with U.S. firms, and it publicly identified what it called front companies involved in Iran's oil trade. The department also identified 20 Iranian financial institutions whose assets are being blocked.
"Iran today is under intense, multilateral sanctions pressure, and we will continue to ratchet up the pressure so long as Iran refuses to address the international community's well-founded concerns about its nuclear program," treasury undersecretary David Cohen said in a news release.
Thursday's actions also were aimed at disrupting the front companies that Iran uses to sell and move its oil, he said.
Western powers fear that Iran may be trying to build nuclear weapons, despite the country's insistence that its nuclear program is for peaceful purposes. The West has been using sanctions and diplomacy to try to stop Iran from producing nuclear arms.
Those sanctions include an oil embargo by the European Union.