By Gerald Butt
Reports said even hardened Israeli paramedics were shocked by the scene
The suicide bombing of an Israeli bus on Tuesday that killed at least 20 people, including women and children, has put the latest peace process, and those committed to it, to their most severe test yet.
The fallout from this atrocity, which was particularly gruesome even by the recent levels of violence in the Middle East, was immediate.
Israel suspended all contact with the Palestinian leadership, sealed off the West Bank and Gaza Strip, and suspended plans to withdraw the army from more Palestinian towns.
For its part, the Palestinian Authority broke off all contact with Islamic militant groups.
This is not a promising formula for a process aimed at building a structure for peace.
The future of the roadmap, therefore, must be in doubt.
The key question is whether Ariel Sharon and Mahmoud Abbas can hold their nerve
The key question will be whether or not the two main political players, prime ministers Ariel Sharon and Mahmoud Abbas can hold their nerve.
The pressure on Mr Sharon from inside Israel - particularly from Jewish settlers and their right-wing supporters in the Likud bloc and other parties who have been critical of the peace process from the start - will be to hit back hard, while that from Washington will be to exercise restraint.
The pressure on Mr Abbas, from Israel and America, will be to crack down on the militant groups ruthlessly and without delay.
'An unthinkable choice'
The Palestinian prime minister is feeling the heat.
After urgent consultations with his advisers in the hours after the Jerusalem bombing, he said the Authority would "stop all forms of dialogue with Hamas and Islamic Jihad.
"It holds them responsible for harming the higher national interest of the Palestinian people," he added.
This is a potentially serious development.
Ariel Sharon's first response was to halt the Israeli pullout from West Bank territories
Up to now Mr Abbas had been counting on winning over the militants through dialogue, in the hope of persuading them not to respond with force to the murder of their leaders by the Israeli security forces.
He has clearly failed and must now contemplate the almost unthinkable choice of ordering his security forces to take up arms against Islamic Jihad and Hamas.
In the meantime, he has ordered an investigation into the bombing.
But this will not be enough to satisfy either Israel or the United States.
President Bush, speaking after the Jerusalem bombing, said the Palestinian Authority needed to "dismantle and destroy" the armed groups.
For now, formally at least, the peace process is still alive - although an Israeli government spokesman said on Tuesday night: "I don't think there was ever a ceasefire."
But pressures on the process in the days ahead could be even more severe.
The less that the Palestinian Authority does to dismantle the militant groups, the more Israel will take steps to try to do so.
That in turn is likely to spark retaliation of the kind witnessed on Tuesday night.
The onus must now be on the United States to urge both sides to give the faltering roadmap yet another chance.
But it is difficult to be optimistic about the chances of success because there appears to be little that Washington can offer to halt the cycle of violence.
Israel is committed to a policy of eliminating Palestinian militants whenever it sees the opportunity.
Hamas and Islamic Jihad, on the other hand, are committed to retaliating every time one of their members is targeted by the Israeli army.
This leaves the Palestinian Authority sitting helplessly in the middle. Aside from the pressures it faces over security issues, the economy is in a state of collapse.
The temperature has never stopped rising for Mahmoud Abbas
The latest closure of the territories will make living conditions even more difficult, with Palestinians unable to cross into Israel to find work.
Mr Abbas, meanwhile, is in the unenviable position of being damned, both by Israel and the United States, if he does not take action against Hamas and Islamic Jihad, as well as by his own community if he orders moves that trigger a civil war in the West Bank and Gaza Strip.
The Palestinian leader faces a chronically difficult choice - but he can not put off the moment of truth much longer.
Against this background, the Bush administration is likely to repeat its commitment to the roadmap.
It knows that neither side in the conflict will want to say publicly that it has been torn up.
Nevertheless, if the violence continues on the scale of the past few days, no-one will be able to pretend the map is worth the paper it is drawn on.