London: Prime Minister Theresa May has repeated the UK government’s deep regret over the Jallianwala Bagh massacre to mark the 100th anniversary of the British colonial era attack in Amritsar on Vaisakhi. The massacre took place at Jallianwala Bagh in Amritsar (undivided Punjab) during the Vaisakhi festival on April 13, 1919, when troops of the British Indian Army under the command of Colonel Reginald Dyer opened fire at a crowd of people holding a pro-independence demonstration, leaving scores dead.