UN Secretary-General Ban Ki-moon has announced that the UN inspectors investigating an alleged chemical weapons attack will be leaving Syria on Saturday, and has asked for time for them to be able to complete their investigation.

Speaking in Vienna on Thursday, Ban said the inspectors would complete their investigations by Friday, and leave the country a day later, at which point they would make a report to him.

Some of the inspectors will personally take samples to laboratories around Europe after leaving Damascus. UN spokesman Farhan Haq said the team's final report will depend on lab results, and that it could take "more than days."

Responding to heightening tensions around the possibility of a foreign military intervention in response to the alleged use of chemical weapons, Ban said that all opinions should be heard before anyone made decisions on how to react.

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Ban's comments came as the team reached Douma, outside Damascus, to examine sites where activists say rockets loaded with chemical weapons struck on August 21.

Aid agencies say at least 355 people were killed and as many as 3,000 injured after the attacks.

The UN inspectors were due to run tests on samples taken from the site and to conduct interviews with the wounded during their visit to Douma.

Ban said that he had spoken with US President Barack Obama, who on Wednesday said that the US government had "concluded" that chemical weapons had been used, and that it was the Syrian government who deployed them, regarding how to "expedite the process of investigation".

"I have also expressed [my] sincere wish that this investigation team should be allowed to continue their work as mandated by the member states," Ban told reporters.

"I told [Obama] that we will [...] share information and our analysis of samples and evidence with members of the Security Council and United Nations members in general," he said.

Source: Al Jazeera and agencies