WASHINGTON - The Obama administration on Wednesday expanded the US sanctions on Iran by tightening up economic measures against the Islamic republic and adding more names to its blacklist.

Under key provisions of the Iran Threat Reduction and Syria Human Rights Act of 2012 that went into effect on Wednesday, the United States will expand the scope of sanctionable transactions with the Central Bank of Iran and other blacklisted Iranian financial institutions, with a view to limiting Iran's ability to use oil revenue held in foreign financial institutions and preventing repatriation of these funds to Iran.

"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 US Department of the Treasury said in a statement.

However, the tightening restrictions exempt the sale of agricultural commodities, food, medicine or medical devices to Iran, the department said.

Washington and its European allies have announced additional measures against Iran's financial institutions and oil exports since late 2011 over Tehran's refusal to give up its uranium enrichment activities, which the West suspects are used to develop nuclear weapons.

On top of further moves against Iran's oil industry, the US Treasury, along with the State Department, also blacklisted one Iranian national and four Iranian entities for their alleged involvement in the Iranian government's censorship activities.

"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," Treasury stated.

Those blacklisted are the Islamic Republic of Iran Broadcasting and its director, Ezzatollah Zarghami, as well as the Iranian Cyber Police, Communications Regulatory Authority and Iran Electronics Industries.

The fresh sanctions came as Iran just agreed to hold new talks with the so-called P5+1 group, consisting of Britain, China, France, Russia, the United States and Germany, on February 26 in Kazakhstan over its controversial nuclear program. Tehran insists that the program is for civilian purposes only.

The two sides held three rounds of talks last year, but failed to make any breakthrough.

"Our policy is clear -- 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, the US Treasury's under secretary for terrorism and financial intelligence.