A soldier allegedly shot dead two of his colleagues before killing himself in the cantonment area of Dharamshala early on Monday, police said.Jasbir Singh, a soldier of the 18 Sikh Regiment, shot dead two fellow soldiers, Hardeep Singh and Harpal Singh, at the Officer's Mess around 2 a.m on Monday.He then shot himself with his service INSAS rifle, police said.All three died on the spot.The Army and the local police are investigating the matter. The reason for the killings is yet to be ascertained.Dharamshala is around 250 km from Chandigarh.