Iran must take urgent action to allay mounting international concerns over its nuclear drive, EU foreign affairs chief Catherine Ashton said Thursday after talks among the major powers.

"We discussed at length the need for Iran to take action urgently as we considered the Iranian nuclear issue," Ashton told reporters after the talks with the foreign ministers of Britain, China, France, Germany, Russia and United States.

The meeting took place after Israel's Prime Minister Benjamin Netanyahu demanded the international community set "a clear red line" to stop Iran getting a nuclear bomb, in a speech at the UN headquarters.

There has been mounting speculation that Israel is planning a military strike on Iran's nuclear facilities.

The European Union's foreign policy chief, who engages with Iran on behalf of the international powers, said she updated the foreign ministers on her talks with Iran's chief negotiator Saeed Jalili in Istanbul last week.

"I will from that meeting now be in touch with Iran to continue this process," Ashton added.

A senior US official, speaking on condition of anonymity, said Ashton will discuss "possible next steps" raised by the ministers.

France's Foreign Minister Laurent Fabius said the meeting had been short because the major powers were united in the Iran crisis.

"We agreed that the main word is 'unity,' unity and to exert pressure," Fabius told reporters.

"What is very important is that the five permanent members of the Security Council plus Germany are completely united on the behavior we have to have toward Iran."

The senior US official also said the international group "is completely united in ensuring that Iran does not acquire a nuclear weapon."

The six nations have pursued a dual track of applying pressure through sanctions while holding talks with Iran's government, which denies that it is trying to develop a nuclear weapon.

Western officials say, however, that Iran is stonewalling in the negotiations. UN ambassadors for the United States, Britain and France have warned that time is running out for a negotiated settlement.

"We believe it is necessary for Iran to understand that there are consequences to their not addressing the concerns of the international community. And we believe that it also helps create space for diplomacy which is far away the preferred way to deal with this issue," the US official said.

Iran's President Mahmoud Ahmadinejad this week shrugged off the threat of an Israeli strike. But pressure has mounted following speeches at the UN General Assembly by US President Barack Obama and Netanyahu.

"The United States will do what we must to prevent Iran from obtaining a nuclear weapon," Obama warned.

Netanyahu called for a "clear red line" to stop Iran enriching enough uranium to make a bomb.