Speaking at an informal meeting of EU foreign ministers, EU foreign policy chief Javier Solana said the bloc is watching to see if Iran would comply with a deadline this week set by the International Atomic Energy Agency (IAEA).

He noted that the UN nuclear watchdog's board of governors is set to meet on September 19 in Vienna, after a September 3 deadline for Iran to stop work on making atomic power reactor fuel that could also be used to make weapons.

"Then we'll see," Solana told reporters, adding that the EU would like to avoid escalating the situation "but (it would) be ready to go to theSecurity Council if necessary, yes."

The United States suspects that the Islamic republic is trying to develop nuclear weapons, and has long threatened to refer the issue to the UN Security Council.

But the European bloc resisted that call, and launched negotiations with Tehran -- offering trade and other benefits in exchange for pledges on its nuclear plans -- after striking an accord with it in Paris last November.

Those talks however broke down last month after Iran ignored calls not to resume sensitive nuclear activities.

"We are very very disappointed. We have been offering a lot to the Iranians. We again call on the Iranians that they come back to the negotiating table," said EU external relations commissioner Benita Ferrero-Waldner.

Other EU sources said that the warning from Solana about refering Tehran to the UN was not a threat.

"Today is not a day for ultimatums," said one, while another added: "The main aim is to persuade Iran to come back to the negotiating table."