Syria asked U.N. Secretary-General Ban Ki-moon on Wednesday to appoint an independent mission to investigate an alleged chemical weapons attack that the regime has blamed on rebels in northern Syria.

The rebels have denied the government claim and blamed regime forces for Tuesday s missile attack on Khan al-Assal village in northern Aleppo province. The Syrian National Coalition, the main opposition group, also demanded an international investigation Wednesday.The U.S. ambassador to Syria, Robert Ford, said Wednesday the Obama administration has no evidence so far to support Syria s accusations, or that a chemical weapons attack occurred at all.

If confirmed, the attack would be the first time a chemical weapon was used in Syria s two-year-old civil war.Syria s U.N. Ambassador Bashar Ja afari told reporters that he asked Ban "to form a specialized, independent and neutral technical mission to investigate the use by the terrorist groups operating in Syria of chemical weapons yesterday against civilians in the town of Khan al-Assal in Aleppo."The Syrian government, which refers to the rebels as "terrorists," said 31 people were killed and more than 100 wounded in the missile attack.

Ja afari called the attack "very serious and alarming and unacceptable and unethical." He said Syria asked the secretary-general for assistance "in a sign of good faith, good will, good intentions" to the international community and the Syrian people.U.N. spokesman Martin Nesirky said Ban has received a written request from Syrian authorities and it is being studied.He reiterated earlier that the secretary-general remains convinced that the use of chemical weapons by any party under any circumstances would constitute "an outrageous crime."

Ban spoke to Ahmet Uzumcu, director general of the Organization for the Prohibition of Chemical Weapons, on Tuesday and both expressed deep concern at the allegations of chemical weapons use. He said the organization is monitoring the situation.Ja afari recalled that Syria sent a letter to Ban and the U.N. Security Council in December warning that rebel groups might use chemical weapons and then blame the government."The Syrian government, if it has such weapons, will never use it against its own population," Ja afari said.

He stressed that Syria is a party to most U.N. conventions on chemical, biological and nuclear weapons and had proposed a Security Council resolution in 2003 when it was a council member that would have required the Mideast to be free of all weapons of mass destruction. He said it was blocked by the threatened veto of an "influential member," an apparent reference to the United States, Israel s closest ally.