UN Secretary General Ban Ki-Moon has said that Syria's president Bashar al-Assad "has committed many crimes against humanity".
He added that he expects a report by UN weapons inspectors to confirm that chemical weapons were used in Syria.
The Secretary-General has accused the Security Council of suffering from an "embarrassing paralysis" on Syria and called on the international community to overcome the deadlock.
Ban Ki-Moon says he is considering asking the UN Security Council to demand Syria immediately transfer chemical weapons to safe sites where they can be destroyed.
UN Secretary-General Ban Ki-moon has appeared to question the legality of US plans for military action in Syria saying that the use of force is only legal in self-defence or with Security Council backing.
He also added that if the UN inspectors confirm the use of chemical weapons in Syria, the Security Council should overcome its differences and take action.
"If confirmed, any use of chemical weapons by anyone under any circumstances will be a serious violation of international law and outrageous war crime," he told reporters. "Any perpetrators must be brought to justice. There should be no impunity."
Ban Ki-moon has said that an attack by the US to punish alleged Syria chemical weapons use could unleash more turmoil in the region.
Samples taken by UN weapons inspectors from the site of an alleged chemical attack in Syria have been sent to laboratories for testing and will arrive "within hours," a UN spokesperson has said.
Since the return of the Mission last Saturday, the UN team worked around the clock to finalise the preparations of the samples in view of their shipment to the designated laboratories.
The samples were shipped this afternoon from The Hague and will reach their destination within hours.
The designated laboratories are prepared to begin the analyses immediately after receipt of samples.
Secretary General Ban Ki-Moon has held talks with the chief inspector, Dr. Ake Sellström, about how the tests can be sped up and will brief members of the Security Council on Tuesday.
The UN Secretary General Ban Ki-moon returned to New York on Thursday evening and intends to engage with member states on developments in Syria, a spokesperson said.
His first meeting is due take place with the permanent members of the Security Council.
United Nations Secretary-General Ban Ki-moon said the chemical weapons team sent to Damascus to investigate alleged chemical attacks will leave Syria by Saturday morning.
He added that the experts would continue their investigations until Friday.
UN inspectors need four days in Syria to conclude their investigation into last week's alleged chemical attack and analyse their findings, UN Secretary-General Ban Ki-moon has said.
"They are working very hard, under very, very dangerous circumstances," Ban said. "Let them conclude their work for four days, and then we will have to analyse scientifically with experts and then I think we will have to report to the Security Council for any actions."
A team of United Nations inspectors has reached rebel-held territory outside Damascus as UN Secretary-General Ban Ki-moon cautioned against pre-empting the chemicals investigation.
Activists confirmed the inspectors had reached the town of Maleiha and were being escorted to towns where deadly gas strikes are alleged to have happened.
Ban's message came as leaders in the west plotted taking military action against the Assad regime over the alleged attacks.
"It is essential to establish the facts," he said from the Hague. "A UN investigation team is now on the ground to do just that. Just days after the attack, they have collected valuable samples and interviewed victims and witnesses. The team needs time to do its job."
UN Secretary General Ban Ki-Moon has said he is confident that weapons inspectors can get evidence about an alleged chemical attack in Damascus despite the passage of time, a spokesman said.