BEIJING - China dampened expectations of further sanctions on Iran Thursday, telling other major powers that putting even more pressure on Tehran would not persuade it to halt its nuclear program.

The five permanent members of the U.N. Security Council, and Germany, told Iran Wednesday to prepare a serious response by October 1 to demands it halt its nuclear program, or face the consequences.

The ultimatum came after U.S. President Barack Obama made his first speech to the General Assembly, urging leaders to join him in confronting world issues including Iran's nuclear plans.

Obama has also said he and Russian President Dmitry Medvedev agreed this week that further U.N. sanctions would be considered if Iran fails to respond to proposals to end a nuclear standoff.

British Prime Minister Gordon Brown, speaking to BBC TV in New York, before a U.N. Security Council meeting on nuclear non-proliferation, said on Thursday:

We'll be particularly telling Iran it's got a decision to make. It can work with the international community, we can help it get civil nuclear power, but if it persists with this course it's going to be isolated from the whole international community.

A British Foreign Office spokeswoman said the window of opportunity for Iran would not be open indefinitely.

October 1 is a key test when the Iranians must demonstrate their commitment to addressing the nuclear issue, she said.

What Iran does will set the context for the coming months...That could be a period in which we seriously consider further sanctions, or it could be the time for serious negotiation with Iran to find a mutually acceptable solution... The choice is Iran's to make.

CHINA UNEASY

But China, traditionally ambivalent about bringing international pressure to bear on other nations and which imports large amounts of crude oil from Iran, signaled that it would be uneasy with a heavy-handed approach.

We believe that sanctions and exerting pressure are not the way to solve problems and are not conducive for the current diplomatic efforts on the Iran nuclear issue, Foreign Ministry spokeswoman Jiang Yu told a regular news briefing in Beijing.

Chinese Foreign Minister Yang Jiechi, in comments to the official Xinhua news agency also repeated China's stance that the issue of Iran's nuclear program was best resolved peacefully through dialogue.

Foreign ministers from the six nations who signed off on the letter to Tehran had met at the United Nations to continue discussions about Iran's disputed nuclear program, which the West suspects is aimed at developing atomic weapons.

In Vienna, the U.N. International Atomic Energy Agency (IAEA) has been urging Iran to explain Western intelligence reports suggesting Tehran has conducted research into building a nuclear warhead.

Iran says the intelligence is fabricated. It insists its nuclear ambitions are limited to the peaceful generation of electricity and has rejected Security Council demands that it suspend all sensitive nuclear activities.

Iranian President Mahmoud Ahmadinejad, in his U.N. address Wednesday, did not directly mention the nuclear issue.

Supreme Leader Ayatollah Ali Khamenei accused the West on Thursday of plotting against the Islamic Republic, but he also said the possibility of military conflict was very low, state television reported.

An exiled Iranian opposition group said Thursday it had identified two previously unknown sites where it said Iran is working on developing high-explosive detonators for use in atomic bombs.

The Paris-based National Council of Resistance of Iran (NCRI) said the sites were part of a unit affiliated with Iran's ministry of defense called Research Center for Explosion and Impact, known under its Farsi language abbreviation Metfaz.

The NCRI's information could not be verified.

The NCRI, with thousands of followers in Europe and the United States, exposed Iranian uranium enrichment research in 2002 that had been hidden from the IAEA. Its subsequent record on reporting Iranian nuclear activity has been spotty.

(Additional reporting by Lou Charbonneau and Parisa Hafezi at the UNITED NATIONS; James Mackenzie in Paris, Mark Heinrich in Vienna, Adrian Croft in London and Tehran bureau; Writing by Samia Nakhoul; Editing by Jon Boyle)

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