The United States unleashed a fresh wave of sanctions against Iran Thursday, ratcheting up pressure to convince Tehran to take seriously concerns about its suspected nuclear weapons program.

The actions impose additional sanctions on Iran's nuclear and ballistic missile proliferation networks and identify Iranian "front" companies and banks to assist in compliance, the Treasury Department said.

"The Treasury and State Department actions target more than 50 entities tied to Iran's procurement, petroleum, and shipping networks," the Treasury said.

David Cohen, the Treasury's under secretary for terrorism and financial intelligence, said the moves take "direct aim at disrupting Iran's nuclear and ballistic missile programs as well as its deceptive efforts to use front companies to sell and move its oil."

"We will continue to ratchet up the pressure," he said.

Iran has been subject to severe international economic sanctions over its controversial nuclear program, which Western powers believe masks an atomic weapons drive despite repeated denials by Tehran.

The increasing pressure from President Barack Obama's administration is designed "to convince Iran to engage seriously and address the international community's concerns about its nuclear program," the Treasury said.

The sanctions freeze Iranian assets under US jurisdiction and prohibit Americans from doing business with the targeted individual or entity.

The United States and European Union have implemented an oil embargo against Iran, leading to a substantial decline in exports of crude from which the Islamic republic draws two-thirds of its foreign exchange earnings.

"The impact on Iran is not just on the barrels that it's no longer selling. It's also in the increasing difficulty that Iran is having in gaining access to the revenue that it's earning," a senior administration official said.

In Thursday's actions, the US Treasury and State departments targeted 11 entities, including a university, and four people, alleging that many of them are part of a network of proliferators headed by Iran's Ministry of Defense for Armed Forces Logistics and its subsidiary, Aerospace Industries Organization.

The four individuals hit with sanctions are: Austrian national Daniel Frosch; Ali Fadavi, Islamic Revolutionary Guards Corps navy commander; Hamid Reza Rabiee, a software engineer; and Hossein Tanideh, a procurement agent for Iran's nuclear program.

The Treasury also said it was acting to prevent the circumvention of international sanctions on Iran -- including sanctions on oil trade with Iran -- by publicly exposing numerous Iranian front companies, ships and banks that are part of the government of Iran.

Among the entities identified were four "front" companies for the Naftiran Intertrade Company or the National Iranian Oil Company: Petro Suisse Intertrade Company SA; Hong Kong Intertrade Company; Noor Energy (Malaysia) Ltd.; and Petro Energy Intertrade Company.

It also identified the National Iranian Tanker Company as an Iranian government entity and, for the first time, the NITC fleet and various front companies belonging to NITC.

It blacklisted 20 Iranian financial institutions.

"These identifications highlight Iran's attempts to evade sanctions through the use of front companies, as well as its attempts to conceal its tanker fleet by repainting, reflagging, or disabling GPS devices," the department said.

"They will assist US persons in complying" with the sanctions, the Treasury said.

They also were aimed at facilitating compliance around the world with US and international sanctions, it said, "including the European Union's prohibition on the import of Iranian oil that went into effect on July 1."