In Jammu and Kashmir, an Indian JCO and three Pakistani soldiers were killed in first major violation of ceasefire in Keran sector in north Kashmir.The troops from the two sides traded heavy gunfire.The key Keran sector is the major ingress route of the militants from across the border.Defence spokesman Lt Colonel J S Brar said while the first exchange of fire took place at 2000 hours on Thursday, the second ceasefire violation took place at 1100 hours today. He said heavy mortars and machine guns were used during firing.