The 12 companies, and 13 individuals, have been added to an existing blacklist of 23 companies and 27 people. Five Iranian nationals are also banned from entering and passing through Switzerland, the country's Federal Council said in a statement.

Switzerland will also ban the delivery of so-called "dual use" materials that could be used for the manufacture of nuclear plants, and the export of some drones and missiles, the statement said.

The UN Security Council last month imposed its third set of sanctions against Iran in the space of 15 months to punish Tehran's refusal to suspend uranium enrichment, which world powers fear Iran could use to make nuclear weapons.

The resolution gives Iran three months to comply with demands to suspend uranium enrichment, and includes an outright ban on travel by officials involved in Tehran's nuclear and missile programmes, as well as broadening a list of individuals and entities subject to an assets freeze.

Switzerland's own trade and diplomatic relations with the Islamic Republic have come under fire in recent months after foreign minister Micheline Calmy-Rey travelled to Tehran in March to sign a gas deal.

Jewish-American group the Anti-Defamation League took out full-page advertisments in Swiss and international papers earlier this month accusing Switzerland of "funding terrorism" through the deal, a charge vehemently rejected by Bern.

The ADL placed advertisements headed, "Guess who is the world's newest financier of terrorism? Switzerland," in the International Herald Tribune, The Wall Street Journal and The New York Times earlier this month.

Israel and the United States also criticised the deal between Iran's state gas firm and Switzerland's Elektrizitaets-Gesellschaft (EGL) Laufenburg, whereby Iran will reportedly supply 5.5 billion cubic metres (194 trillion cubic feet) of gas annually from 2011.

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