Pakistani troops have been firing artillery guns across the Line of Control in Jammu and Kashmir and the Indian Army is responding, sources said on Thursday, in dramatic escalation of hostilities on a day three Indian soldiers lost their lives in shelling. The ceasefire violation started last night as Pakistan launched unprovoked firing in the Mankote and Krishna Ghati sectors, a defence spokesperson said. Two soldiers were killed in firing by Pakistan in the Nowgam sector of Kupwara district in North Kashmir early this morning.