The US and Russia have failed to agree a date for a Syrian peace conference.
The two countries remain divided over what role Iran might play in talks to end the civil war and over who would represent Syria's opposition.
"We were hoping that we would be in a position to announce a date today; unfortunately we are not," said UN-Arab League envoy Lakhdar Brahimi.
Mr Brahimi chaired the meeting at the United Nations in Geneva.
"But we are still striving to see if we can have the conference before the end of the year," he said.
Mr Brahimi conferred with senior US and Russian officials before widening the talks to include representatives from Britain, France and China.
He also included Syria's neighbours Iraq, Jordan, Lebanon and Turkey, as well as the Arab League.
Mr Brahimi said he would bring Russian and US officials together again on 25 November.
He said he hoped that opponents of Syrian President Bashar al-Assad would have agreed on delegates to represent them some days before that.
"The opposition has a very, very difficult time," he said.
"They are divided. It is no secret for anybody. They are facing all types of problems and they are not ready."
Russian Deputy Foreign Minister Gennady Gatilov, who met Mr Brahimi along with fellow Deputy Foreign Minister Mikhail Bogdanov, said the US did not have the leverage needed to assemble a credible opposition delegation representing various factions.
"It is not just the representation of the opposition that is required, but the participation of an opposition delegation of a broad range of opposition forces. And this is what the Americans are failing to achieve," RIA news agency quoted him as saying.
The US was represented at the talks with Mr Brahimi by State Department Under Secretary Wendy Sherman and Robert Ford, the US ambassador to Syria.
The proposed peace conference is meant to build on a June 2012 agreement among world powers in Geneva that called for a transitional authority with full executive powers, but did not explicitly say Mr Assad should step down.
UN warns over 9m Syrians need humanitarian aid
The United Nations estimates that around 9.3m people in Syria, or about 40% of the population, need humanitarian assistance due to the country's civil war.
"The humanitarian situation in Syria continues to deteriorate rapidly and inexorably," UN humanitarian chief Valerie Amos told the UN Security Council behind closed doors, according to her spokeswoman Amanda Pitt.
"The number of people we estimate to be in need of humanitarian assistance in Syria has now risen to some 9.3 million," Ms Pitt said, summarising Ms Amos's remarks to the 15-nation council.
"Of them, 6.5 million people are displaced from their homes, within the country."
The population of Syria is around 23 million.
"Amos continues to press the council for their help and influence over those parties who can ensure the protection of civilians and civilian facilities; the safe passage of medical personnel and supplies; the safe and unhindered delivery of humanitarian assistance; and can facilitate progress in expanding critical, life-saving relief operations," Ms Pitt said.
Ms Amos's plea to the council follows the Syrian government’s promise yesterday to ensure delivery of vaccinations and humanitarian aid across the country.
It comes after an outbreak of polio in the northeast and warnings of malnutrition in areas under military siege.
Twenty-two children in Deir al-Zor province bordering Iraq were left paralysed last month.
The polio virus has been confirmed so far in ten of them and experts say it could spread quickly across the region.
Last month, Ms Amos demanded stronger action by the Security Council to get desperately needed aid into Syria, where millions of people in need have not received any help for almost a year.
Violence and excessive red tape have slowed aid delivery to a trickle in Syria.
More than 100,000 people have been killed in the civil war and millions have fled the country in the past two-and-a-half years.
After months of talks, the 15-member Security Council approved a non-binding statement on 2 October urging increased humanitarian access.
Ms Amos has complained that that statement has had little impact on the ground.
