The United Nations said on Thursday it will investigate Syria's allegations that rebel forces used chemical weapons in an attack near Aleppo, but Western countries sought a probe of all claims about the use of such banned arms.

"I have decided to conduct a United Nations investigation into the possible use of chemical weapons in Syria," Secretary-General Ban Ki-moon said. He told reporters the investigation will focus on "the specific incident brought to my attention by the Syrian government."

Syria asked Ban to investigate an alleged chemical weapons attack by "terrorist groups" near the northern city of Aleppo on Tuesday, Syrian U.N. Ambassador Bashar Ja'afari said.