Israeli security forces have found the bodies of three teenagers who were abducted in the West Bank earlier this month and confirmed them as the Israeli seminary students sought since 12 June.
Israeli Prime Minister Benjamin Netanyahu summoned his security cabinet for a special session that could decide on stronger military moves against Hamas, which has neither confirmed nor denied the Israeli allegations.
Mr Netanyahu has blamed Hamas "animals" for killing the three.
"They were kidnapped and murdered in cold blood by animals in human form," his office quoted him as saying. "Hamas is responsible and Hamas will pay."
"There can be no forgiveness for the killers of children and those who sent them. Now is the time to act," Economy Minister Naftali Bennett said in a statement.
The kidnapping on 12 June of the three Jewish seminary students near a settlement in the West Bank appalled Israelis who rallied behind the teens' families.
Mr Netanyahu seized on the abduction to demand Western-backed Palestinian President Mahmoud Abbas abrogate a reconciliation deal he reached with Hamas, his long-time rival, in April that led to a unity Palestinian government on 2 June.
The bodies of Gil-Ad Shaer and US-Israeli national Naftali Fraenkel, both 16, and Eyal Yifrah, 19, were found in a field near Hebron, a militant stronghold and the hometown of two Hamas members identified by Israel as the kidnappers and still at large.
The teens had apparently been shot soon after having been abducted while hitchhiking, the officials said.
"They were under a pile of rocks, in an open field," said Lieutenant-Colonel Peter Lerner, a military spokesman.
Israeli media said the break in the case came after the relatives of the alleged abductors were interrogated.
A large number of troops gathered at the spot - in the general area where the teenagers disappeared - to recover the bodies.
Since January, six Palestinian children have been killed by Israeli forces, according to the NGO Defence for Children International - Palestine.
In tandem with the search over the past 18 days, Israeli forces have raided Palestinian towns and villages, detaining Hamas activists and closing the group's institutions.
Mr Abbas condemned the abduction and pledged the cooperation of his security forces, drawing criticism from Hamas and undercutting his popularity among Palestinians angered by what they saw as his collusion with Israel.
The United States, while condemning the kidnapping, has urged Israel to pursue a measured response.
Hamas, which has maintained security control of Gaza since the unity deal, is shunned by the West over its refusal to renounce violence.
The group has called for Israel's destruction, although various officials have at times indicated a willingness to negotiate a long-term ceasefire.