Three Palestinian armed groups say they were involved in Sunday's attack on the main border between Israel and Gaza: Hamas, Islamic Jihad, and the al-Aqsa Brigades.
The al-Aqsa Brigades are linked to Yasser Arafat's Fatah movement. Palestinian Prime Minister Mahmoud Abbas - commonly known as Abu Mazen - is himself a long standing Fatah member.
This illustrates the scale of the problem Abu Mazen faces as he tries to curb the activities of Palestinian militants. They have reinforced their rejection of a cease-fire by uniting to strike at an Israeli target.
Sunday's shooting was the first major attack since the peace summit
The location is significant. The area next to the Erez crossing where the attack took place has been occupied by Israeli forces since the middle of last month. They moved in to stop Hamas fighters launching rockets at nearby Israeli targets.
Troops have uprooted vast areas of orchards which they say the militants were using as cover. They have destroyed the family homes of people suspected of involvement in attacks on Israelis.
Hamas and the other groups were infuriated by Abu Mazen's statement at the end of the Middle East summit in Aqaba on 4 June.
They found his pledge to end the armed intifada - or uprising - particularly unacceptable.
They say the Palestinian prime minister gave too much weight to Israeli concerns.
They were angered by his failure to mention the status of Jerusalem, or the fate of refugees from the 1948 Arab-Israeli war and their descendants - two of the enduring questions for Palestinian nationalists.
The Palestinian militant groups are not alone in their implacable opposition to the latest plan for peace in the Middle East, which is known as the roadmap.
Jewish settlers turned out in Jerusalem in their thousands in the hours following the Aqaba summit.
One demonstrator summed up his view as follows: "Talking to the Palestinians now is like the United States talking to Osama Bin Laden after 11 September."
The first phase of the roadmap for Middle East peace does call on the Palestinians to crack down on militants.
It also calls on the Israelis to end the demolition of Palestinian homes and property.
Abu Mazen's pledge to end violence has angered militants
Abu Mazen now faces pressure from both the militants and the Israelis.
An Israeli Government spokesman, Avi Pazner, has warned that the Palestinian prime minister must deal with the armed groups immediately.
"If he doesn't fight the terrorists, we will," the spokesman added.
Abu Mazen does not enjoy large scale popular support - not yet, at least.
Many Palestinians are weary of the conflict, but doubtful that the roadmap can really bring a lasting peace.
Much Israeli opinion is equally cynical.
They have seen too many plans fail in the past.
Looking for benefits
If the Palestinians are to give Abu Mazen the support he needs to carry it through in the longer term, they will want to see tangible benefits.
So far they have not.
In the wake of the shootings, and other security warnings, the Israelis have tightly reinforced restrictions on movement in and out of the West Bank and Gaza which were slightly eased a week ago.
The timing of the attack may affect whether Israel honours its summit pledge to begin dismantling settlement outposts in the West Bank.
Hamas had earlier broken off ceasefire talks with Abu Mazen
The Israeli Government has not ruled out a military response.
Nobody on either side of the conflict expected the beginning of the roadmap's implementation to be straightforward. Neither did the plan's international sponsors.
At the end of the Aqaba summit, President Bush conceded "The journey ahead is difficult, but there is no other choice."
Extremists on both sides remain to be convinced.