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.
The three, all students at a Jewish seminary, went missing late Thursday as they were hitchhiking between Bethlehem and Hebron.
"We believe that they have indeed been kidnapped by presumed Palestinians," a senior officer told journalists, without giving further details on who was behind the abduction.
He said the search is being carried out in coordination with security forces from the Palestinian Authority, and that "tens of Palestinians" have been arrested in the process.
He added that 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.
Troops also 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 a Palestinian unity government early last week.
A rocket was fired from Gaza into Israel early Saturday without causing any casualties or damage, the army said.
In response, Israel carried out air strikes on southern Gaza "hitting a site of terrorist activity and a weapons depot," an army statement said.
The Palestinian movement Hamas in Gaza 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 any 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 that 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.
Another Palestinian official said the authority's security services were "cooperating" with Israeli agencies to gather information on the teenagers' disappearance.