Britain has suggested imposing U.N. sanctions on Iran unless it allays suspicions about its nuclear program, but Russia and China remained at odds with Europe and the United States Monday night on the best way to confront Tehran.

Senior diplomats from six key nations convened for a 4 1/2-hour meeting to discuss how to persuade Iran to stop enriching uranium, the radioactive material that can be used to make a nuclear weapon. But they still could not overcome Russian and Chinese opposition to tough action in the U.N. Security Council.

The meeting, hosted by British Foreign Office Director John Sawers, occurred hours after a letter came to light detailing Britain's approach to Iran. The confidential document from Sawers suggested a blend of threats and enticements, starting with a Security Council statement and then moving to a legally binding resolution demanding Iran halt uranium enrichment.

It would introduce a package of incentives as a way of getting Russia and China onboard, and if Tehran fails to allay fears that it may be developing nuclear weapons, push "further measures" — possibly including sanctions, according to the letter obtained by The Associated Press.

But Monday evening's meeting appeared to achieve little, with officials from all sides saying that talks would continue. The immediate disagreement, which the Security Council has grappled with for a week, is over a proposed council statement urging Iran to abandon uranium enrichment and calling for a report in 14 days.

The Security Council has scheduled consultations on the statement Tuesday afternoon and U.S. Ambassador John Bolton had expressed hope it could be adopted at the end of the meeting.

But U.S. Undersecretary of State Nicholas Burns told reporters after Monday's meeting that further discussions were needed.

"It may take a little bit of time, but it's going to be worth the time because when we do achieve that statement, it will be yet another clear unified message by the international community" Burns said.

The six countries present — the United States, Russia, China, Britain, France and Germany — differ on the best way to get Tehran to halt uranium enrichment, which can be used either to generate electricity or to produce nuclear arms.

The British hoped the Russians and Chinese would agree to tougher council action if necessary in exchange for Western willingness to engage in new negotiations, according to the letter and U.N. diplomats.

Moscow and Beijing want the U.N. nuclear watchdog agency, the International Atomic Energy Agency, to assume the main role in cajoling Iran on enrichment and its refusal to fully cooperate with an IAEA probe. They also contend that 14 days is too short for a progress report on Iran's compliance.

After Monday's meeting, China's U.N. Ambassador Wang Guangya reiterated his stance that Beijing could agree to Security Council action "if it is a short, brief political statement."

The March 16 letter stressed the importance of showing Iran that "more serious measures are likely" if it doesn't stop enriching uranium — possibly including a legally binding resolution that cound be enforced by military means. But it acknowledged the challenge that negotiators will face in getting Russia and China onboard, and suggested a package of proposals to entice Iran.

"We are not going to bring the Russians and Chinese to accept significant sanctions over the coming months, certainly not without further efforts to bring the Iranians around," the letter said.

It was addressed to Burns, German Foreign Office Political Director Michael Schaefer and French Foreign Ministry Political Director Stanislas de Laboulaye.

Russia and China have said tough council action could spark an Iranian withdrawal from the Nuclear Nonproliferation Treaty.

The United States, Britain and France want a statement listing demands already made by the IAEA — including the suspension of uranium enrichment and steps toward greater transparency and more cooperation.

Negotiations between Iran and France, Germany and Britain collapsed in August after Tehran rejected incentives offered in return for a permanent end to enrichment. Its subsequent moves to toward enrichment capabilities led the IAEA to ask for Security Council involvement earlier this year.