Israel’s Defence Minister said on Saturday that the military is determined to find the three missing teenagers, one of whom is an American, who he said are presumed alive and believed held by Palestinian militants.

Security forces searched the West Bank for a second day on Saturday, looking for three missing teenagers who disappeared late on Thursday in the West Bank, reportedly while hitchhiking.

Troops arrested more than a dozen Palestinians in connection to the case and are also examining footage from security cameras.

If confirmed that the three teenagers, aged 16 and 19, were seized by Palestinian gunmen, it would be the biggest kidnapping by such militant groups in recent memory in the West Bank.

Israeli-Palestinian tensions already were strained at the time of Thursday’s suspected kidnapping, in part because of the recent formation of a Palestinian unity government that has the backing of the Islamic militant group Hamas.

Israeli Defence Minister Moshe Yaalon said on Saturday that Israel has thwarted dozens of kidnapping attempts by militants, including 14 so far this year.

“It appears this event slipped under our radar, but we will not rest until we free the youths and put our hands on the terrorists who are responsible for this operation,” Mr. Yaalon said.

“As long as we don’t know otherwise, our working assumption is that they are alive,” he said.

Israel’s government held Palestinian President Mahmoud Abbas responsible for the fate of the teens.

“The current crisis is a direct result of the decision by Palestinian President Mahmoud Abbas to force a political alliance with these Hamas terrorists,” said Mark Regev, a government spokesman.

Palestinian officials also rejected Israel’s attempts to blame Mr. Abbas, noting that Israel retains overall security control in the West Bank.

Despite the charged rhetoric, Palestinian security forces were cooperating with Israeli counterparts in trying to find the teens, a Palestinian official said.

Mr. Abbas has said security coordination in the West Bank between Israel and the Palestinians, usually aimed at tracking down Islamic militants, will continue despite the unity government.

Meanwhile, three different claims of responsibility emerged in the West Bank, though it’s not clear if any were authentic.

In one leaflet, a group portraying itself as a branch of an al-Qaeda splinter group said it kidnapped the three to avenge the killing of three fighters by Israeli security forces earlier this year.

Israel’s military has warned soldiers and civilians not to accept rides from strangers, but hitchhiking remains common.

An Israeli intelligence official said more than 50 kidnapping attempts were thwarted at various stages of execution in 2013 alone. Palestinians have kidnapped Israelis before but this would be the first time they abducted three civilians at the same time. The official spoke anonymously as he is not allowed to brief the media.

Israeli authorities clamped a partial gag order on the case. Israeli media have been reporting the incident almost non-stop. On Saturday, local media published the names of the teens and their home communities.

Two of the three missing teens are from settlements in the West Bank, territory Israel captured from Jordan in the 1967 Mideast war and that Palestinians are demanding as part of their future state along with the Gaza Strip and east Jerusalem.

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