The Obama administration on Wednesday added Iranian individuals and firms to a blacklist, as the United States and Europe tighten the screws on Iran's nuclear program a week after UN sanctions.

The new US sanctions target insurance companies, oil firms and shipping lines linked to Iran's atomic or missile programs as well as the Islamic Revolutionary Guards Corps (IRGC) and Iran's defense minister Ahmad Vahidi.

Under the steps taken, "all transactions involving any of the designees and any US person are prohibited, and any assets the designees may have under US jurisdiction are frozen," the Treasury Department said.

During a summit Thursday in Brussels, European Union (EU) leaders are expected to approve their bloc's curbs on investment as well as transfers of technology, equipment and services in Iran's oil and gas industry.

The EU proposals also target the Islamic Republic's transportation, banking and insurance sectors.

Last Wednesday the UN Security Council slapped its fourth set of sanctions on Iran, authorizing high-seas inspections of vessels believed to be ferrying banned items to Iran and adding 40 entities to a list of people and groups subject to travel restrictions and financial sanctions.

In introducing fresh US sanctions on Wednesday on behalf of President Barack Obama's administration, Treasury Secretary Timothy Geithner said the United States was indeed urging other countries to follow suit.

"We have been working behind the scenes, building international support among finance ministries, for additional actions to prevent abuse of the global financial system by Iran," he said.

The US Congress was also set to join the fray.

Howard Berman, chairman of the House Foreign Affairs Committee, welcomed the new US sanctions, saying they will "significantly extend the reach of comprehensive Iran sanctions legislation that Congress will soon pass."

The new sanctions are designed for broader effect than bolstering the US arsenal against Tehran as the United States already prohibits practically all business dealings with Iran and its citizens.

"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," Geithner said.

Geithner told reporters that Iran's Post Bank -- the 16th Iranian-owned bank added to the blacklist -- was designated for its alleged support of proliferation activities.

The measures also target the IRGC Air Force and IRGC Missile Command, which are suspected of having ties to Iran's ballistic missile program, according to the Treasury Department.

Also sanctioned are:

-- Rah Sahel and Sepanir Oil and Gas Engineering Co. "for their ties to previously designated Khatam al-Anbiya Construction Headquarters.

-- Two individuals for their roles in the IRGC.

-- Two individuals and two entities for their ties to Iran's WMD programs, including Javedan Mehr Toos, a procurement broker for Kalaye Electric Company.

-- Five Islamic Republic of Iran Shipping Lines (IRISL) front companies.

Among other individuals targeted are Javad Karimi Sabet, who has been linked to the Atomic Energy Organization of Iran, and Mohammad Ali Jafari, the commander in chief of the IRGC since September 2007.

Geithner said the Obama administration has identified a total of 22 petroleum, energy and insurance companies located both inside and outside Iran "that are owned or controlled by the Iranian government."

The State Department's special advisor for non-proliferation and arms control Robert Einhorn told reporters he hoped the new sanctions will make Iran conclude "it is in their best interests to come to the negotiating table."

The United States has long offered Iran trade and other incentives in exchange for halting its uranium enrichment program, which western powers fear masks a drive to build a nuclear bomb.

Iran claims its aims are peaceful.

In leading the US push for penalties at the UN Security Council, Secretary of State Hillary Clinton told opponents of sanctions that Iran will only negotiate seriously when it feels the bite of sanctions.

Arguing that diplomacy needed more time to work, Brazil and Turkey last week voted against the sanctions and Lebanon abstained as the 12 remaining members of the Security Council voted for them.