VIENNA/TEHRAN/WASHINGTON: A senior U.N. nuclear agency team will visit Tehran on Jan. 28 with Iran saying it is ready to discuss allegations that it was involved in secret nuclear weapons work after years of refusing to do so, diplomats said Thursday. The news came as Ali Larijani, the influential speaker of Iran’s parliament, said during a visit to Turkey that his country was ready for “serious” talks with world powers on its controversial nuclear program.

In comments reported by the official IRNA news agency, Larijani said: “The negotiations can yield results if they are serious and not a game.”

But he noted an offer made last week by Turkey to host the talks between Iran and the five permanent members of the U.N. Security Council, plus Germany, and said “we have given our agreement” to that proposal.

Iran has several times said it is willing to resume those talks, which collapsed a year ago.

Iran insists its nuclear program is for exclusively peaceful purposes but most Western countries believe it masks a drive to develop nuclear weapons – a suspicion strengthened by a November report by the International Atomic Energy Agency which stated for the first time that some of the alleged experiments can have no other purpose than developing nuclear weapons.

Two diplomats told the Associated Press that Iranian officials had suggested they were ready to talk about the issue during recent meetings with officials of the Vienna-based IAEA. The developments came after an assassination in Tehran Wednesday of a nuclear scientist and increased Western sanctions on Iran’s economy.

Iran’s Supreme Leader, Ayatollah Ali Khamenei, said that those behind the killing would be punished, the official IRNA news agency reported.

“We will continue our path with strong will ... and certainly we will not neglect punishing those responsible for this act and those behind it,” Khamenei was quoted as saying.

Iran accuses Israel and the U.S. of being behind the assassination of scientist Mostafa Ahmadi Roshan, who was killed by a bomb attached to his car by a passing motorcyclist Wednesday, and insisted it will not disrupt its nuclear ambitions.

“If Israel thinks they can prevent our studies with four terrorist attacks, it’s a very weak way of thinking ... Everybody will learn that they can’t stop us with such actions,” Larijani told a news conference at Iran’s embassy in Ankara.

U.S. Secretary of State Hillary Rodham Clinton denied any U.S. role in the slaying and the U.S administration condemned the attacks.

The U.S. and its allies are pressuring Iran to halt uranium enrichment, which a former U.N. inspector Olli Heinonen said could provide Iran with the ability to have enough such material for one nuclear bomb early next year – though it was not clear it would yet have the ability to build one.

President Barack Obama signed laws on New Year’s Eve that, by denying buyers access to U.S. dollars, aim to cripple Iran’s oil sales until it gives ground on the nuclear issue. U.S. allies in Asia and Europe have voiced support for Washington’s drive to cut Iran’s oil exports, though fear of self-inflicted economic pain is curbing enthusiasm for an embargo.

Japan pledged to take action to cut its oil imports from Iran in response to an appeal for support from visiting U.S. Treasury Secretary Timothy Geithner.

Finance Minister Jun Azumi said Japan buys 10 percent of its oil from Iran. “We would like to take action concretely to further reduce in a planned manner,” he said. But he added: “It would cause immense damage if they were cut to zero.”

The U.S. State Department Thursday announced sanctions on China’s state-run Zhuhai Zhenrong Corp. which it said was the largest supplier of refined petroleum products to Iran.

Clinton also imposed sanctions on Singapore’s Kuo Oil Pte Ltd. and FAL Oil Company Ltd., an independent energy trader based in the United Arab Emirates, the State Department said in a notice.

One issue affecting Asian governments’ willingness to follow the U.S. lead is the availability of alternatives to Iran, the second biggest exporter in OPEC after Saudi Arabia. While ready to help, it is not clear how far U.S. ally Riyadh can increase its own output and exports to make up for spurned Iranian crude.

Japan has already sought extra supplies from Saudi Arabia and the United Arab Emirates. China’s Premier Wen Jiabao will visit Saudi Arabia, the UAE and Qatar in a trip beginning this weekend. The prime minister of South Korea, another major buyer of Iranian crude, is due to visit the UAE and Oman Friday.

India faces pressure to cut Iran crude purchases, but policymakers and industry officials have sent mixed messages on future plans with one unnamed Cabinet minister saying the country would continue to do business with Tehran.

The European Union is more sympathetic to U.S. pressure on Iran. EU foreign ministers are expected to agree on a ban on imports of Iranian crude oil on Jan. 23.

“We expect a slow and gradual implementation of what will eventually become a full embargo,” said Mike Wittner from Societe Generale. “Europe has the same concerns about its fragile economy and an oil price spike as the U.S., probably even more.”