Burma finally signs the international convention, though it has been accused of using and manufacturing chemical weapons in recent years.
Burmese military officials have called on their Thai counterparts to help capture Kokang rebel leader Peng Jiasheng who they claim is hiding in Thailand.
Kokang rebels allege that the Burmese army have continued attacks on their positions, despite the declaration of a unilateral ceasefire earlier this month.
Chinese Ambassador Yang Houlan said Beijing made contact with MNDAA leader Peng Jiasheng to seek an end to the hostilities.
The MNDAA has vowed to stop attacking Burmese government units as from Wednesday at midnight, other than for self-defence.
Violence between ethnic armies and government forces has reached an impasse with the KIA and MNDAA both reporting more violence.