UNITED NATIONS: Information provided by Syria, Britain and France on alleged chemical weapons attacks in Syria will be "crucial" in deciding the scope of the investigation the U.N. is planning, U.N. diplomats said.

Secretary-General Ban Ki-moon sent a letter to the U.N. Security Council on Friday indicating the possibility of a broader investigation, the diplomats said, speaking on condition of anonymity because the letter has not been made public.

The secretary-general received a letter from the Syrian government Wednesday requesting an independent probe of a purported chemical weapons attack on Tuesday on Khan al-Assal village in northern Aleppo province. He received a letter from France and Britain on Thursday asking for an investigation into that alleged attack, as well as two others.

Ban said Thursday that investigators would look into Syria's allegation that rebels carried out a chemical weapons attack but said he was aware of allegations of other, similar attacks. The rebels blamed regime forces for the Aleppo province attack.

A U.N. diplomat quoted Ban's letter to the Security Council on Friday as saying he has asked Syria, Britain and France "to provide additional information pertaining to the incidents they have reported to me."

"The provision of this information will be crucial in deciding the terms of reference for the mission and the scope of its work with a view to verifying any alleged use of chemical weapons in Syria," the diplomat quoted the letter as saying.

The secretary-general ended the letter stressing "the importance of receiving the fullest cooperation from all relevant authorities" in Syria, the diplomat said.

Syria is widely believed to have a large stockpile of chemical weapons. The government has not confirmed it, saying only that it would never use chemical weapons against its own people.

Western nations fear President Bashar Assad would use chemical weapons if he sees the two-year civil war turning against his government. But they are equally concerned that rebel forces, including some linked to al-Qaida, could get their hands on unguarded chemical weapons or the materials to make them.

In their letter to Ban, France and Britain raised allegations of chemical weapons use in two locations in Khan al-Assal and the village of Ataybah in the vicinity of Damascus on Tuesday, and in Homs on Dec. 23. The letter, obtained by The Associated Press, asked the U.N. chief to launch "an urgent investigation into all allegations as expeditiously as possible."

A U.S. administration official said Thursday that the U.S. has strong indications that chemical weapons were not used in the attack in Aleppo province on Tuesday.