UNITED NATIONS, Dec. 13 -- UN chief Ban Ki-moon on Friday called for holding accountable those responsible for using chemical weapons in Syria.

He made the appeal after a UN investigation team found that such weapons were used on several occasions at multiple sites against both civilians and military targets.

"The international community has a moral and political responsibility to hold accountable those responsible, to deter future incidents and to ensure that chemical weapons can never re-emerge as an instrument of warfare," Ban said while presenting the team's final report to the UN General Assembly.

"We must also do our utmost to achieve universal adherence to the Chemical Weapons Convention. I urge all States that have not yet done so to sign, ratify and accede to this vital instrument without delay," said the secretary-general.

The team did not specify which party might have used the weapons in the nearly three-year-old conflict between the government and rebels, and that is not within the team's mandate.

The Syrian government has acknowledged the possession of chemical arms, joined the Chemical Weapons Convention, and pledged their elimination.

The newly-founded Joint UN Mission with the Organization for the Prohibition of Chemical Weapons (OPCW) is overseeing the destruction of Syria's stockpiles and production facilities.

The team, which had in September found "clear and convincing evidence" of Sarin gas attacks against civilians, including children, in the Damascus area, this time reported "credible information" that such weapons were used against soldiers and civilians in other parts of the country, including in Khan Al Asal on March 19.

But in this latter case as with three other incidents -- in Jobar on Aug. 24, in Saraqueb on Aug. 24, and in Ashrafiah Sahnaya on Aug. 25 -- the release of chemical weapons could not be independently verified.

The team visited the site of a relatively large scale Sarin attack on Aug. 21 in the Ghouta area of Damascus, and found evidence.

However, the team could not establish a link between victims, alleged event and alleged site at the other sites, which it did not visit, due to lack of primary information on delivery systems and environmental samples collected and analyzed under the chain of custody.

It based its Ghouta findings on Sarin found in exploded surface-to-surface rockets, environmental contamination by Sarin in the area where patients were affected, epidemiology of over 50 interviews by survivors and health care workers, and blood and urine samples that were positive for Sarin.

"I deplore in the strongest possible terms the use of chemical weapons in Syria as an offense against the universal values of humankind," Ban said.

"The international community continues to expect that the Syrian Arab Republic will implement faithfully its obligations related to the complete elimination of its chemical weapons programme by the first half of 2014, and that it will abide by global norms on disarmament and nonproliferation."

With well over 100,000 people already killed in Syria, mostly with conventional weapons, the secretary-general underlined his determination to seek an urgent end to the conflict.

"Nearly half the population of Syria is either displaced or in need of urgent humanitarian assistance," he said. "The conflict is having profound impacts on the stability and economy of the entire Middle East."

"As Syrians prepare to work for a political solution at next month's conference (in Geneva) on Syria, I appeal to all parties to demonstrate their leadership and vision by ceasing hostilities and instead working to meet the legitimate aspirations of the Syrian people as they seek freedom and dignity," he said.

"I call on the international community to do everything in its power to achieve this outcome," Ban added.