Israeli Prime Minister Benjamin Netanyahu has vowed retaliation against the suspected Hamas militants for the slayings of three Israeli teenage boys who were found dead in the West Bank city of Hebron this week, CNN reported.

Citizens across Israel on Tuesday mourned the deaths of 19-year-old Eyal Yifrach, 16-year-old Gilad Shaar and Naftali Fraenkel, also 16. All three are suspected to have been killed by the Palestinian militant group Hamas after being kidnapped on June 12, a claim the militant group denies.

But it appears Israel has already condemned Hamas for the killings, with Netanyahu telling his Cabinet the murderers will not go unpunished.

"Vengeance for the blood of a small child, Satan has not yet created," said the prime minister, who is expected to deliver a eulogy at the boys' funeral on Tuesday, according to CNN. "Neither has vengeance for the blood of three pure youths who were on their way home to their parents who will not see them anymore."

Hundreds of Palestinians said to have ties to Hamas were arrested last month during the Israeli Defense Forces search for the boys in the West Bank.

"Hamas is responsible and Hamas will pay," Netanyahu said. "May the memories of the three boys be blessed. They were abducted and murdered in cold blood by human animals."  

Israeli has already increased military action against Hamas in Gaza. Monday night saw fire and explosions as dozens of key Hamas targets were hit, CNN reported. The airstrikes were carried out after 18 rockets were launched into Israel on Sunday, the station reported.

The Palestinian news agency Wafa said a 21-year-old Palestinian man was killed "in cold blood" in the West Bank. Israeli forces said they open fired at a suspected Hamas terrorist who threw a grenade at them.

Hamas warned "the gates of hell will open" if Netanyahu "brings war on Gaza," according to CNN. The group maintains it was not responsible for kidnapping or killing the boys.