The CPI-M on Tuesday urged the government to take steps to end border infiltration after three terrorists sneaked into a Punjab town and went on a killing spree.Condemning Monday's terror attack in Dinanagar town, the Communist Party of India-Marxist said: "This attack by a three-member squad, reportedly coming from across the border in Pakistan, is a matter of serious concern."It is to be investigated how such a squad could cross the border which is fenced and patrolled. "The security forces must take the necessary steps to foil such cross border infiltration. The intelligence apparatus must be beefed up to ensure that such incidents do not recur."The terrorists killed seven people, including a superintendent of police, in Dinanagar on Monday before they were shot dead by security forces.