The IDF spent its third day searching for three abducted Israelis by expanding its operations on Sunday against Hamas in the Hebron region. The wave of arrests included Hamas leader Hassan Yousuf, who was arrested in Hebron.The efforts took covert and overt forms, and included attempts to dupe the enemy, a senior security source said Sunday."Our working assumption is that the teenagers are alive. We are working to bring them back alive," he said.In addition to close cooperation with the Shin Bet and other security agencies, the IDF's Central Command has received large-scale operational assistance from General Staff, in the form of the deployment of field intelligence units and special forces to the area.Hebron has been under closure since Saturday evening in what the source described as a "partial geographic isolation." The closure is not total, in order to avoid harming Palestinian civilians, the source added."We have a lot of knowledge on Hamas in Hebron," the source said. "Dozens of kidnappings attempts have been thwarted [this year]," he added. "There is a knowledge infrastructure, and the Shin Bet has intelligence assessments [on the kidnappers]," said the source.Hamas in the West Bank is in a difficult situation, the source continued, saying the organization is struggling in general to carry out suicide bombings and kidnappings despite attempts. "It is under pressure. At the same time, that's not enough to lower its motivation," he added.The motivation for terrorists to carry out terror attacks remains very high.The closure around Hebron is not harming its economy, according the source.He described the kidnapping as "an incident with the potential for escalation. Our set challenge is to prevent an escalation.""I hope this [operation] will be short, but we are prepared for a long operation," he added.