UNITED NATIONS — Syria's Western-backed opposition group urged a U.N. team heading to Syria in the coming days to start their investigation of alleged chemical weapons use in a village near Aleppo where rebel fighters recently ousted government forces.

The Syrian National Coalition said in a statement Friday that it sent a letter to U.N. Secretary-General Ban Ki-moon reiterating its offer of "full cooperation with the investigation team, particularly in assuring their unfettered access into liberated areas."

The U.N. gave approval Wednesday for the investigation of three allegations of alleged chemical weapons use. The decision followed an understanding reached between the Syrian government and U.N. disarmament chief Angela Kane and chief chemical investigator Ake Sellstrom, who visited Damascus last week.

The U.N. only identified Khan al-Assal, a village on the southwestern outskirts of Aleppo, which was captured by the rebels last week and was under attack by government forces this week. The government and rebels have blamed each other for a purported chemical weapons attack in Khan al-Assal on March 19.

"As the Free Syrian Army has recently liberated the Khan al-Assal area, we urge the U.N. team to begin its investigation in this area and hope to welcome their arrival without any further delays," the opposition coalition said.

In the letter to Ban, obtained by The Associated Press, the coalition's U.N. representative, Najib Ghadbian, urged the U.N. team to "act without delay to investigate reported incidents of chemical weapons use throughout this area."

"Both the Syrian Coalition and the Supreme Military Council stand ready to cooperate fully with representatives of the mission and welcome U.N. investigators into all territories under our control," the letter said.

U.N. spokesman Martin Nesirky said Thursday the locations of the two other sites to be investigated "are being kept confidential as a safety and security precaution." The two sites were chosen based on an evaluation of available information which indicated "an onsite investigation is warranted," he said.

Nesirky said the chemical weapons experts were gathering in The Hague, Netherlands and will depart "within days" for Syria.

The mandate of the investigation team is to report on whether chemical weapons were used, and if so which chemical weapon, but not to determine the responsibility for an attack.

The letter said the opposition coalition and Supreme Military Council are committed to upholding international humanitarian and human rights laws "and condemn the deployment of chemical weapons."

"We further demand that any individuals found responsible for the use of chemical weapons be held accountable for their crimes, in full accordance with international law," the letter said.