Israel re-arrested 51 Palestinians freed in a 2011 prisoner swap deal, the army said on Wednesday, in the sixth day of a hunt for three missing teenagers believed abducted in the occupied West Bank.Israel accuses Hamas Islamists of kidnapping the seminary students, who disappeared on Thursday while hitchhiking from a Jewish settlement. There has been no word from them since, nor any public claim of responsibility or ransom demands - including by Hamas, though neither has it denied involvement.A military spokesman said more than 65 Palestinians were detained overnight, including 51 who were part of a group of 1,027 prisoners released by Israel three years ago in return for soldier Gilad Shalit, who was seized by Hamas in 2006."We have two efforts ongoing in parallel. First is to bring back the boys, and the second is to take a toll on Hamas for its actions," spokesman Lieutenant-Colonel Peter Lerner said.Palestinians said the majority of those re-arrested were affiliated with Hamas, and accused Israel of reneging on the prisoner-swap deal, which was partially brokered by Egypt."What Israel is doing has nothing to do with security, but is a policy of revenge," said Qadoura Fares, chairman of the Palestinian Prisoners Club, which advocates on behalf of Palestinians in Israeli custody.An Egyptian official said that Cairo, which is in contact with Hamas and other Palestinian factions, was helping Israel gather information that might lead to the missing teenagers. But he denied Israeli and Palestinian media reports that Egyptian mediation was already under way.Palestinian President Mahmoud Abbas, whose unity deal with Hamas in April led Israel to suspend peace talks with him, said those responsible for the kidnapping had only brought an Israeli military crackdown upon Palestinians in the West Bank."Regardless of the party that did this, we will have to say that to them, because we can't tolerate such operations," Abbas said at a summit of the Islamic Conference Organisation, in Jeddah."We are coordinating with (Israel) in order to return those youths because they are human beings and we want to protect the lives of human beings," said Abbas, who held a rare telephone conversation with Israeli Prime Minister Benjamin Netanyahu on Monday.