The United States, Britain and France warned Iran on Thursday that time is running out for a negotiated settlement to the showdown on its nuclear program.
"Time is wasting," US ambassador Susan Rice told a UN Security Council meeting on nuclear sanctions against Iran.
Iran is "at a crossroads," Britain's UN envoy Mark Lyall Grant told the meeting at which western nations also slammed Iran for its arms deliveries to Syria and alleged links to terrorism.
The meeting was held amid mounting speculation that Israel is planning a military strike on Iran's nuclear facilities. Iran's President Mahmoud Ahmadinejad is to speak at the UN General Assembly of world leaders next week.
A series of reports by the International Atomic Energy Agency, the UN nuclear watchdog, have said Iran is stepping up uranium enrichment and not providing proof that its nuclear activities are peaceful.
The western powers say Iran is seeking a nuclear bomb but the Tehran government says its drive is peaceful.
No Iranian diplomat spoke at the meeting where Rice said the international powers -- Britain, China, France, Germany, Russia and United States -- cannot pursue their nuclear talks with Iran "indefinitely".
"We will not engage in an endless process of negotiations that fail to produce any results. We must therefore remain clear and united in seeking resolution of the international community's concerns regarding Iran's nuclear program. Time is wasting," the US envoy said.
Top officials from the six international powers are to meet in New York next week to discuss Iran. But Russia and China have spoken against tightening the four rounds of UN sanctions already imposed.
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Rice said "Iran's approach remains to deny, to deceive and distract."
She called on UN members, particularly neighbors of Iran, to step up action to halt Syria's arms shipments to President Bashar al-Assad's forces in Syria. UN sanctions experts have uncovered evidence of shipments and diplomats said that Iran is sending some weapons by air across Iraqi territory.
States in the region must "redouble their efforts to deny, inspect and seize illicit Iranian shipments, including transfers by air corridors," Rice said.
The US government has asked Iraq to ensure that Iranian planes flying over its territory land and face cargo inspections, amid concerns that arms are being shipped to the Assad government.
Britain's UN ambassador called the arms exports to Syria "a reminder of Iran's hypocrisy in claiming to support freedom in the Arab world."
"The Iranian regime is at a crossroads," said Lyall Grant.
"It can continue to ignore the international community's concerns over its nuclear program, or it can negotiate a settlement that will help to realize the benefits of a civil nuclear program.
"It can support the oppressive regime in Syria in suppressing freedom, or it can play a constructive role in its region. It can be an exporter of terrorism or a responsible member of the international community. But it must make these choices soon," Lyall Grant said.
France's UN ambassador Gerard Araud said: "We are asking Iran to negotiate, but Iran is not negotiating."