New York  - Major world powers on Wednesday said they expected a serious response from Iran to the international community's concerns over its nuclear programme when the sides meet for talks on October 1.

US President Barack Obama and Russian President Dmitry Medvedev agreed to keep up pressure on Iran and left open the possibility of further sanctions during a meeting on the sidelines of the UN General Assembly in New York.

Foreign ministers from the five permanent members of the UN Security Council - the United States, Russia, China, Britain and France - plus Germany held a meeting later Wednesday to discuss their positions ahead of the October 1 meeting.

"We are united in our willingness to work with Iran on these matters. The meeting on October 1 will provide the opportunity to seek a comprehensive, long-term and appropriate solution to the Iranian nuclear issue through dialogue and negotiation," read a statement from the foreign ministers.

"We expect a serious response from Iran and will decide on the context in our dual-track approach on the result of the meeting of our next step."

Iranian President Mahmoud Ahmadinejad, who addressed the UN General Assembly late Wednesday, made no mention of the nuclear dispute or the October meeting. He has said he considers the nuclear issue closed.

Russia has reluctant to step up pressure on Iran in the past. But Medvedev left the door open, saying the international community had to do its utmost to convince Iran to make the "right decision" and abandon any ambitions for nuclear weapons.

"Sanctions rarely lead to productive results. But in some cases sanctions are inevitable," Medvedev said.

Obama said Iran would be offered a clear choice during the meeting of coming clean on its nuclear programme or face greater international isolation.

"If Iran does not respond to serious negotiations and resolve this issue in a way that assures the international community that it's meeting its commitments, and is not developing nuclear weapons, then we will have to take additional actions," Obama said.

"Sanctions - serious additional sanctions - remain a possibility." (dpa)