Prime Minister Benjamin Netanyahu on Sunday afternoon dismissed Hamas’s denial of involvement in the abduction of yeshiva students Eyal Yifrach, Naftali Frenkel, and Gil-ad Shaar, saying Israel knew “for a fact” that Hamas was responsible.

“Hamas denials do not change this fact. And this attack should surprise no one because Hamas makes no secret of its agenda. Hamas is committed to the destruction of Israel and to carrying out terrorist attacks against Israeli civilians – including children,” he said.

Netanyahu had announced Sunday morning that Hamas was behind the kidnapping of the three teenagers in the West Bank on Thursday night, allegations that were swiftly shot down by a spokesman for the Gaza-based organization as “stupid” and “designed to break Hamas.”

In a briefing to the foreign press Sunday afternoon, the prime minister rejected as “patently absurd” the argument that the Palestinian Authority could not be held accountable for the attack due to the fact that the Gush Etzion region, where the teens were abducted from, was under Israeli security control. The prime minister repeatedly insisted, both in an address Saturday night and in his remarks Sunday, that the PA bears full responsibility for the fate of the three teenagers.

“When an attack takes place in Tel Aviv or in London or in New York – all these places have been attacked by terrorists – the question is not where the attack takes place. The question is where it originated. The kidnappers in this case set out from territory controlled by the Palestinian Authority, and the PA cannot absolve itself of its responsibility,” Netanyahu said.

Three kidnapped Israeli teens, from L-R: Eyal Yifrach, 19, Naftali Frenkel, 16, and Gil-ad Shaar, 16. (photo credit: courtesy)

He added that Israel would spare no effort to bring the boys home.

The prime minister emphasized that Israel had warned the international community of the repercussions of the recent establishment of a Hamas-Fatah unity government of technocrats, and warned that just as Hamas had gained control in Gaza, it would advance terror in the West Bank.

Israel significantly increased its security presence in Hebron on Sunday afternoon as a closure was imposed on the city, where the IDF has concentrated its efforts to hunt down the terrorists. Over 80 Palestinians, including a number of senior Hamas officials, were taken into Israeli custody overnight Saturday.

With the mass arrests and closures in Hebron, Israel’s crackdown on the kidnappers is a “collective punishment against the entire Palestinian people,” a spokesman for the Palestinian unity government said Sunday, according to the Palestinian Ma’an News Agency.

IDF soldiers prepare to search for three kidnapped Jewish teenagers near Hebron, in the West Bank, Saturday, June 14, 2014 (photo credit: Yonatan Sindel/Flash90)

“The Israeli government cannot hold the Palestinians responsible for security in occupied territories which are not under Palestinian sovereignty and which house dozens of settlements and outposts,” Ehab Bessaiso said in a statement.

On Sunday afternoon, concrete blocks were brought to the outskirts of Hebron to block off roads, while bulldozers were deployed along other access routes, the Ynet news site reported. Palestinian sources said that the army was already preventing entry or exit from the city, which lies 30 kilometers (19 miles) south of Jerusalem.

The IDF was also deploying additional troops to the area, where the teens are believed to be held. An additional battalion of infantry forces was sent to Hebron to bolster forces already there and special units that operate observation balloons were also ordered to take up positions overlooking the city.

Hundreds of troops from the Shimshon battalion were reported to have interrupted their training exercises on the Golan Heights and were heading for the West Bank, where they may also be deployed around Hebron. By Sunday afternoon some 2,500 soldiers had been sent to the city, Ynet reported.

Defense Minister Moshe Ya’alon declared a full closure of the city Saturday night, preventing passage of Palestinians through its checkpoints aside from those in need of urgent medical care.

The working assumption by Palestinian intelligence was that Hamas is behind the kidnappings, a suspicion echoed up by Netanyahu’s assertions.

Israeli soldiers search for three Jewish teenagers near Hebron, in the West Bank, Saturday, June 14, 2014 (photo credit: Yonatan Sindel/Flash90)

According to the Palestinian sources, Palestinian intelligence received notice of the kidnapping only 12 hours after the event, and since then has maintained communications with the Israeli side, with active coordination between the two security forces.

Bessaiso, the Palestinian spokesman, appealed to the “international community and all international human rights organizations to protect the Palestinian people against the Israeli escalation.”

Bassaiso condemned the Hebron closures and measures preventing visits to Palestinian political prisoners held in Israel, and “other oppressive procedures.”