The United States and five other world powers will meet Friday in Brussels to discuss what measures can be taken to punish Tehran for its refusal to halt its nuclear enrichment program.

Diplomats in Vienna, meanwhile, said International Atomic Energy Agency inspectors paid a second visit to Iran's recently revealed Fordo uranium enrichment facility on Thursday.

Iran acknowledged Fordo's existence in September in a confidential letter to the U.N. watchdog, then faced sharp criticism from the U.S., Britain and France for hiding the facility for years. Iran says it is building the fortified facility as a backup in case its main plant at Natanz is attacked.

The diplomats spoke on condition of anonymity in exchange for divulging confidential information.

The United States and other nations fear Iran wants to build nuclear arms, but Tehran insists its nuclear program is peaceful.

Friday's meeting will include the U.N. Security Council's permanent members — Britain, China, France, Russia and the U.S. — plus Germany, EU foreign affairs spokeswoman Cristina Gallach said Thursday. She said it would bring together political directors — foreign ministry officials below the ministerial level — from the six nations "to take stock of the situation."

Iran announced Wednesday it would not export its enriched uranium for further processing, effectively rejecting the latest plan brokered by the IAEA. That plan aimed to delay Tehran's ability to build a nuclear weapon by sending most of the uranium needed for that out of the country.

Following Iran's announcement, President Barack Obama said Washington has started talking with its allies about new punishments against Iran. Speaking during a visit to South Korea, Obama said a new package of punitive steps will likely be developed "over the next several weeks." He did not elaborate.

In Kabul on Thursday, U.S. Secretary of State Hillary Rodham Clinton said Washington has taken a dual-track approach to Iran's nuclear program.

"We said we would reach out to see whether or not there could be any common discussions about their nuclear program and other problems that we and other countries in the region have with Iran," she said. "But we also said that there was a second track and that track was to work toward consequences for Iran if engagement did not work. We will proceed accordingly."

But Iranian Foreign Minister Manochehr Mottaki played down the threat of sanctions, saying embargoes have proved ineffective since the 1960s.

"I think they are wise enough not to repeat failed experiences," Mottaki told reporters Thursday in Manila.

The United Nations last month offered a deal to take much of Iran's low-enriched uranium to reduce its stockpile of material that could be enriched to a higher level, and possibly be used to make nuclear weapons.

Iran would export its uranium, which is enriched at less than 5 percent — enough to produce fuel to burn in power plants. Enriching uranium to much higher levels can produce weapons-grade material. In exchange, the Iranian uranium would be further enriched in Russia and then be sent to France. Once there, it would be converted into fuel rods, which would be returned to Iran.

The amount of uranium exported by Iran under the U.N. plan, about 1.2 tons, represents about 70 percent of its stockpile. It would have been sent to Russia in one batch by the end of the year.

That uranium would be returned a year later as refined fuel rods, which can power reactors but cannot be readily turned into weapons-grade material.

"Yesterday, Iran clearly refused the deal," French Foreign Ministry spokesman Bernard Valero said Thursday. "We are going to evaluate with our partners ... the consequences of this political response."

Russia's Deputy Foreign Minister Sergei Ryabkov said he would represent Russia at the talks Friday in Brussels.