UNITED NATIONS – Britain and France have told the secretary-general they have reliable evidence that the Syrian government used chemical weapons near Aleppo, in Homs and possibly in Damascus, U.N. diplomats and officials said on Thursday.

The British and French ambassadors told Ban Ki-moon in a letter on March 25 that soil samples and interviews with witnesses and opposition figures backed their belief that the government used chemical shells that had caused injuries and deaths, the diplomats and officials said.

They spoke on condition of anonymity because the letter has not been made public.

Syria asked Secretary-General Ban Ki-moon on March 21 to investigate an alleged chemical weapons attack by rebels two days earlier on Khan al-Assal village in northern Aleppo province. The rebels blamed regime forces for the attack.