Iran will not stop higher-grade enrichment of uranium in response to external demands, Tehran's top nuclear official was quoted as saying on Tuesday, signaling a tough bargaining stance ahead of planned new talks with world powers.

Western powers want Iran to halt enrichment of uranium to a fissile concentration of 20 percent as it represents a significant step closer to the level that would be required to make nuclear bombs. Iran says it needs uranium refined to 20 percent to run its medical research reactor in Tehran.

Israel has threatened air strikes on Iran if its nuclear work is not curbed through diplomacy or sanctions, raising the spectre of a Middle East war damaging to the global economy.

"The Islamic Republic of Iran will not suspend 20 percent uranium enrichment because of the demands of others," said Fereydoun Abbasi-Davani, head of the Atomic Energy Organisation of Iran, according to the Iranian Students' News Agency (ISNA). "The Islamic Republic of Iran will produce 20 percent enriched uranium to meet its needs and for however long it is required."

He did not specify what he meant by "needs". Western diplomats say Iran already has made sufficient amounts to fuel its Tehran Research Reactor for several years. Abbasi-Davani has in the past said Iran plans to build another research reactor.

"Twenty percent enrichment is the right of the Iranian nation for use in the Tehran reactor and it will defend this right with authority," Abbasi-Davani said.

The European Union quickly responded to his comments, saying Iran must come to grips with increasing international disquiet over the ultimate purpose of its uranium enrichment programme to resolve the protracted dispute.

"Iran has to address the immediate key concern, which is the issue of 20 percent enrichment, by taking an initial comprehensive confidence-building step in this area, thereby creating space for more diplomacy and negotiations," the spokesman for EU foreign policy chief Catherine Ashton said.

Abbasi-Davani signalled renewed Iranian defiance in negotiations with world powers expected to resume soon. But he did not appear to categorically rule out that Tehran at some point could shelve the activity.

Iranian foreign ministry spokesman Ramin Mehmanparast said on Tuesday that Iranian and EU officials had held discussions regarding the time and place of the next negotiations between the powers, known collectively as the P5+1, and Iran.

"If there is an agreement, it will be announced," Mehmanparast said in his weekly news conference.

His statement came a day after the U.S. State Department said Iran had been presented with a specific offer of a date and venue for the next talks but had yet to respond.

Though Israel has threatened to bomb Iranian nuclear facilities, Vice Prime Minister Moshe Yaalon said on Tuesday the Jewish state had noticed renewed U.S.-led efforts to curb Iran's nuclear programme since President Barack Obama's re-election last month, including preparation for possible military action.

He also cited contacts among the powers and Iran about holding new negotiations and ongoing sanctions against Iran.

Iranian media quoted Foreign Minister Ali Akbar Salehi on Tuesday saying that any calls for direct talks between the U.S. and Iran were meaningless as long as Washington continued to exert pressure on Iran through sanctions and other measures.

In October, the New York Times reported that secret exchanges between U.S. and Iranian officials had yielded agreement "in principle" to hold one-on-one talks. Both Iran and the United States denied that the two countries had scheduled direct bilateral negotiations on the nuclear programme.

"They are trying to pursue their unjust goals through an approach of pressure against the Iranian nation," Salehi was quoted as saying by state news agency IRNA. – Reuters