It was a day all those present hoped they would never see.

For nearly three weeks, the prayers of every Israeli, parent and child had had been tied to the desperate belief that "their boys" would be found alive.

But at Modi'in cemetery on Tuesday, the raw grief of the tens of thousands of mourners poured out under the burning sun.

The murders of Naftali Frenkel, Gilad Shaer and Eyal Yifrach were not just personal tragedies. Their families' pain was evident in the face of every person present and the conversation of every Israeli.

As the crowd waited for the triple burial to begin, a spontaneous song broke out from deep in the throng: "May this be a time of mercy."

Within hours, the grief turned to anger. Anti-Arab riots erupted in Jerusalem and, on Wednesday morning, the body of a Palestinian teenager was found in a forest in West Jerusalem, killed in a suspected revenge attack.

Meanwhile, Palestinians held violent demonstrations in East Jerusalem and threw rocks at Israeli forces demolishing the home of a suspect in a separate terror case.

On Thursday, Israel responded with air strikes and began reinforcing its forces along its border with the Gaza Strip after missiles fired from Gaza hit two homes in the town of Sderot, according to reports.

The Modi'in event was one of the largest funerals in Israeli memory, although bereaved families held their own, smaller memorials before despatching the bodies to the cemetery.

At these local events, Naftali Frenkel's father, Avi, said his 16-year-old son had been a victim of antisemitism and joined "millions in our history killed for the same reason". Ofir Shaer, father of 16-year-old Gilad, spoke of his son's "courage" in calling the police for help after being kidnapped. And Uri Yifrah said of his son, Eyal, 19: "You are holy, you were holy in your life. You gave strength to so many people."

Those in the crowd were mostly religious. They had prayed fervently for the teenagers and desperately needed an outlet for their grief.

Esther Zadok, an elderly woman, was crying uncontrollably. "The mother of Gilad works in the school where my husband is the security guard - how can I hug her now?" she asked.

"Everything fell out of me when I heard the news; my heart just fell to the floor," said Roger Mayo, 59, from the Galilee city of Karmiel.

Gila Douadi, 49, from Petach Tikva and one of the few non-religious people at the funeral, said: "Everyone who comes here feels it's their children."

The kidnapping brought an unusual burst of Jewish unity, said Daniel Hool, a 43-year-old Jerusalemite. "I've been in Israel for 28 years and to my mind there has never been an event that has unified Jews here and in the world in the same way as the kidnapping," he said. Mr Hool, a Charedi teacher from London, "screamed out loud in uncontrollable crying" when he heard the bodies had been found.

In Britain, Chief Rabbi Ephraim Mirvis said: "The Jewish people and many others are mourning the loss of three precious souls, taken in the prime of their lives. We stand as one with their families, teachers and friends."

Board of Deputies president Vivian Wineman said: "This is a tragic reminder of the very real security threats Israel's civilians face and we call on the Palestinian Authority to use its full endeavours to ensure that the perpetrators of this shocking crime are brought to justice."

MPs and Peers debated the deaths on Tuesday, with statements and questions in both houses of Parliament.

At Prime Minister's Questions the following day, in response to a question from Robert Halfon MP, Mr Cameron said the murders were "an absolutely appalling and inexcusable act of terror".

More than 600 people gathered for a candlelit vigil outside the Israeli embassy in London on Wednesday to express their solidarity with the bereaved families of the three teenagers.

Naomi Daniel, 20, from Netanya in northern Israel, who is volunteering in the UK for her national service, said: "I feel real emotion being here. There is a strong connection between Jews here in England and in Israel. The Jewish people are very unique in this way."