The United Nations vowed Saturday to give an "impartial and credible" assessment on whether chemical arms were used in Syria as tensions rose over a possible military strike.
But UN spokesman Martin Nesirky said no conclusion can be given on whether banned poison gas had been unleashed in Syria until laboratory tests are completed.
Nesirky also said it was "grotesque" to believe that the departure of UN weapons experts from Syria had opened up a possible window for a missile strike against President Bashar al-Assad's forces.
UN disarmament envoy Angela Kane briefed UN leader Ban Ki-moon on the mission in New York on Saturday.
The UN inspectors have a mandate to report on whether banned chemical weapons have been used in the 29-month-old war in Syria -- particularly during an August 21 attack on an opposition area near Damascus -- but not to say who carried it out.
Following criticism of the UN investigation mission, Nesirky said: "The United Nations mission is uniquely capable of establishing in an impartial and credible manner the facts of any use of chemical weapons."
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Kane told Ban that the UN inspectors were "able to conduct a wide range of fact finding activities," Nesirky told reporters.
The inspectors have taken the samples to The Hague and they will be moved to two laboratories in Europe, Nesirky said.
Ban will speak to the chief inspector, Ake Sellstrom, by telephone on Sunday. But Nesirky said "before the mission can draw any conclusions on this incident the laboratory process must be completed."
Ban said "whatever can be done to speed up the process is being done," according to Nesirky.
According to diplomats, Ban told ambassadors from Britain, France, the United States, China and Russia on Friday that the team would need two weeks to complete a first analysis.
The United Nations still has more than 1,000 international and national staff in Syria and Nesirky said the world body was looking at which staff need to stay there.
But he said it was "grotesque" how some analysts had declared that the departure of the UN inspectors had opened up the possibility of a US military strike.
"It's also an affront to the more 1,000 UN staff who are on the ground in Syria delivering humanitarian aid and who will continue to deliver critical aid," he said.