JERUSALEM - Three Israeli teenagers, one of them also a US citizen, have been kidnapped in the occupied West Bank, presumably by Palestinians, the army said on Saturday.Israeli Prime Minister Benjamin Netanyahu held the Palestinian Authority responsible for their well-being, but Palestinians baulked at the idea they were to blame for the disappearance inside an Israeli-controlled area of the West Bank.The suspected abductions come as Israel piles pressure on a new Palestinian government, formed early last week under a reconciliation deal between the Palestine Liberation Organisation and Israel’s foe, the Islamist movement Hamas. The three, students at two Jewish seminaries, went missing late Thursday as they hitchhiked between Bethlehem and Hebron.They have been named as Eyal Yifrah, 19, and two 16-year-olds, Naftali Frenkel and Gilad Shaer. ‘We believe that they have indeed been kidnapped by presumed Palestinians,’ a senior officer told journalists, without elaborating on who was behind the abduction.He said the search is being carried out in coordination with security forces from the Palestinian Authority, and ‘tens of Palestinians’ have been arrested in the process. He added substantial reinforcements had been brought in, including special forces and an airborne brigade, to participate in the search around Hebron, in the southern West Bank.Israeli Defence Minister Moshe Yaalon visited the site of the disappearance. ‘Because we have no information to the contrary, we are assuming that they are still alive,’ he told reporters. Troops closed the main crossings into the Gaza Strip to prevent the teenagers from being smuggled into the territory, where the Islamist Hamas movement remains dominant despite the formation of the Palestinian unity government.A rocket was fired from Gaza into Israel early on Saturday, followed by three more in the afternoon, none of which caused any casualties or damage, the army said. In response, Israel launched air strikes on southern Gaza, ‘hitting a site of terrorist activity and a weapons depot’, an army statement said. Hamas said Apache gunships had fired on a training camp of its armed wing in Khan Yunis and empty ground in Rafah, on the Egyptian border, without causing casualties.Prime Minister Benjamin Netanyahu spoke with US Secretary of State John Kerry Friday, and said he holds Palestinian president Mahmud Abbas responsible for the teenagers’ safety. Kerry also telephoned Abbas, a Palestinian source said. A spokesman for the Palestinian Authority’s security services, General Adnan al-Damiri, called Netanyahu’s suggestions ‘mad’.Damiri said the PA had no authority over the sprawling Gush Etzion settlement bloc, which is under full Israeli control. ‘Even if there was an earthquake, Netanyahu would blame the Palestinian Authority,’ he told AFP. Israel has held Abbas responsible for all violence emanating from Gaza and for West Bank security since he signed a reconciliation deal with Hamas and the new government was formed.Another Palestinian official said the authority’s security services were ‘cooperating’ with Israeli agencies to gather information on the teenagers’ disappearance. A statement in Arabic attributed to the jihadist Islamic State of Iraq and the Levant (ISIL) group claimed the kidnapping late on Friday. The statement’s authenticity could not be verified, however, and it contained spelling errors.