Paris: French Foreign Minister Alain Juppe said on Tuesday he was convinced that Iran was developing nuclear weapons and called for the EU to impose tougher sanctions on Tehran.

"Iran is pursuing the development of its nuclear arms, I have no doubt about it," he told a news channel.

"The last report by the International Atomic Energy Agency is quite explicit on this point."

"This is why France, without closing the path of negotiation and dialogue with Iran, wants stricter sanctions," he added.

He said French President Nicolas Sarkozy has proposed a freezing of assets of Iran's central bank and an embargo on exports of Iranian oil, a move also being considered by the European Union.

"The American Congress has backed this idea and President (Barack) Obama has just signed it into law and we hope that the Europeans, by January 30, take equivalent measures to show our determination," Juppe said.

Obama on Saturday signed into law tough new sanctions targeting Iran's central bank and financial sector, in a move that could intensify a brewing Gulf showdown.

Tensions have risen in recent days after Iran – which insists its nuclear programme is purely for peaceful purposes -- test-fired a series of missiles near the key Gulf oil supply route of the Strait of Hormuz.

The European Union meanwhile said on Tuesday that Iran must respond to an EU letter before nuclear talks can resume, and dismissed a call by Tehran for the bloc to set a new date for negotiations.

EU Foreign Policy Chief Catherine Ashton, who represents six world powers in the talks, has yet to receive a response to a letter to Iranian nuclear negotiator Saeed Jalili in October offering to resume negotiations.

"We wrote to them saying in broad terms, if you want to show that your nuclear programme is peaceful, then we are happy to listen to that and that will involve discussions," Ashton's spokesman said.

An Iranian foreign ministry spokesman said Tehran was waiting for Ashton to set a date and venue to resume talks with the United States, Britain, France, Germany, Russia and China.