The Israeli prime minister, Binyamin Netanyahu, has accused the Islamic militant group Hamas of being behind the kidnapping of three teenagers – including a US citizen – who went missing nearly three days ago, as Israeli troops tightened their grip on the southern West Bank and rounded up scores of Palestinians.
While Israel extended its dragnet around Hebron on Sunday, sealing off most entrances to the city, troops clashed with Palestinians on the streets of Ramallah in which a 20-year-old protester was killed and another wounded, witnesses and hospital officials said.
Israel and Hamas continued to traded accusations on Sunday, with the Islamist group denying it was behind the kidnapping, despite some members welcoming it.
The US secretary of state, John Kerry, condemned the kidnapping of the boys, issuing a statement calling for the release of Gil-ad Sha'er, Eyal Yifrach and Naftali Frankel and apparently backing Israeli claims of Hamas involvement.
"We are still seeking details on the parties responsible for this despicable terrorist act, although many indications point to Hamas's involvement," Kerry said.
"As we gather this information, we reiterate our position that Hamas is a terrorist organisation known for its attacks on innocent civilians and which has used kidnapping in the past."
Amid rapidly rising tensions in the West Bank, the Israeli military flooded the Hebron area with several thousand additional troops, deployed extra anti-rocket units in two southern cities and called up several hundred reservists.
The kidnapping and the scale of the operation to recover the boys and root out those responsible, is one of the most serious security incidents in recent memory.
Amid the vast manhunt, Israeli soldiers have swamped Palestinian villages around Hebron and in effect closed off the city. Reinforcements of paratroopers were drafted in to makeshift camps circling the city, and observation balloons launched to help with the search.
In the village of Beit Einoun, Israeli soldiers searched through a barn on Sunday, kicking through the hay in animal pens watched by the owner.
In another villager's home, soldiers searched balconies and rooms, as a crowd observed from a distance.
"Why are they doing this?" said a man named Marwan. A youth in a Real Madrid football shirt, who declined to give his name, added: "Do they think the missing boys are in this neighbourhood?
"They are only here because a burned-out car [which it has been suggested was linked to the kidnapping] was found two kilometres away.
"They are trying to put pressure on us and put pressure on the Palestinian government."
The search has been accompanied by widespread arrests – about 80 Palestinians were seized on Sunday, including dozens of members of Hamas swept up in overnight raids. Palestinian officials put the number of people taken into custody by Israeli authorities so far at more than 100, including seven Hamas members of the newly forged Palestinian parliament and several prisoners recently released by Israel.
In nearby Haloul, close to the entrance to Hebron, Fadi al-Hadobyi said soldiers had come during the night to confiscate video footage from the closed-circuit television cameras in central Hebron and made multiple arrests.
As he described the previous evening's activities, several young Palestinian men darted past the entrance to his shop pursued by Israeli army vehicles and a group of soldiers on foot, the sound of teargas canisters and plastic-coated bullets being fired echoing behind them.
With no obvious progress in the hunt for the three missing youths, who were abducted while hitchhiking home from their religious schools in West Bank settlements, the focus has turned to an alleged failure by police to pass on the alert for as much as five hours, according to some reports.
Israel's police service has come under fire for ignoring for several critical hours a desperate phone message from one of the teenagers, who called an emergency line on Thursday night and said: "We're being kidnapped."
Speaking to his cabinet on Sunday, Netanyahu said only one group should be held accountable.
"Those who perpetrated the abduction of our youths were members of Hamas, the same Hamas that Abu Mazen [the Palestinian president, Mahmoud Abbas]made a unity government with. This has severe repercussions," he said.
The Hamas leadership has furiously denied Netanyahu's allegations, which were described by a spokesman as "stupid". Other Hamas members praised the apparent kidnapping but stopped short of accepting responsibility.
The crisis has fed into already heightened tensions between Israel and the new Palestinian government, headed by Abbas but backed by Hamas.
Netanyahu has condemned Abbas's agreement with the militant group, and said he would hold him responsible for the youths' safety.
The prime minister's attempts to use the fate of the missing teens to score wider political points have not gone uncriticised in the Israeli media. Barak Ravid observed in the left-leaning Haaretz newspaper on Sunday: "Netanyahu increased the intensity of [his] attacks, saying the kidnapping was the result of the new unity government and holding Abbas responsible. Netanyahu knows full well that no one is quite buying that."
Palestinian militants have repeatedly threatened to kidnap Israelis, hoping to use them as bargaining chips to win the release of prisoners held by Israel. This would be the first incident when three civilians have been taken at the same time.
