The gunmen approached the checkpoint dressed as soldiers
Palestinian gunmen have killed four Israeli soldiers in an attack near the main crossing point between the Gaza Strip and Israel.
The attack on the Erez army checkpoint - in which the three gunmen were themselves shot dead - came just hours after Palestinian militants vowed to maintain their campaign of violence against Israel.
Three groups took joint responsibility for the attack, in what is seen as a serious blow to Palestinian Prime Minister Mahmoud Abbas, who pledged to crack down on militants at a US-led peace summit on 4 June.
The Israeli army said the gunmen, wearing military uniform, approached the army post and opened fire, killing the four Israeli soldiers and wounding four others before being killed.
A BBC correspondent in Jerusalem, Richard Galpin, says the attack - claimed by Hamas, the Islamic Jihad, and the Al-Aqsa Brigades - leaves the new Palestinian prime minister in "an extremely difficult position".
ROADMAP MAIN POINTS
Phase 1 (to May 2003): End to Palestinian violence; Palestinian political reform; Israeli withdrawal and freeze on settlement expansion; Palestinian elections
Phase 2: (June-Dec 2003) Creation of an independent Palestinian state; international conference and international monitoring of compliance with roadmap
Phase 3 (2004-2005): Second international conference; permanent status agreement and end of conflict; agreement on final borders, Jerusalem, refugees and settlements; Arab states to agree to peace deals with Israel
Israeli government spokesman Avi Pazner said Mr Abbas "had to deal with the issue of terrorism immediately and not wait a single day" in the wake of the attack.
"We don't expect to see 100% results immediately, but if he does not fight the terrorists, we will," he said.
Following the attack, Mr Abbas - widely known as Abu Mazen - postponed a planned trip to Gaza aimed at pushing for a ceasefire.
Palestinian militants had earlier endorsed a decision by Hamas to break off ceasefire talks with the prime minister.
Our correspondent says they have been infuriated by Abu Mazen's pledges to end the armed uprising against Israel, and in response they have united to strike at an Israeli target.
The Egyptian Government is reported to be discussing the possibility of sending its intelligence chief, General Omar Suleiman, to try to restore the stalled dialogue between the various Palestinian factions.
Problem for peace plan
On Saturday evening, the Israeli army sealed off the West Bank - preventing Palestinians from crossing into Israel.
Military officials said the measure followed "heightened and numerous terror alerts".
One of the groups claiming responsibility for the attacks, the al-Aqsa Brigades, is linked to Yasser Arafat's Fatah movement, of which Abu Mazen is himself a long-standing member.
The BBC's James Rodgers in Gaza says this illustrates the scale of the problem the Palestinian prime minister faces as he tries to curb the activities of armed groups.
Our correspondent says Israel has made it clear that the peace process cannot advance while such attacks continue.
The Gaza meeting brought together Hamas, Islamic Jihad, the Popular Front for the Liberation of Palestine, the Democratic Front for the Liberation of Palestine and Fatah.
"We decided to pursue the armed intifada because we reject the conclusions of the Aqaba summit, where resistance was equated with terrorism," Mohammed el-Hindi of the Islamic Jihad told AFP.
Four Israeli soldiers were wounded in the attack
A Hamas spokesman said his group would resume the ceasefire talks only if Abu Mazen withdrew his statement made at Aqaba.
However, this is widely viewed as an impossible condition for the prime minister to meet.
Abu Mazen has accepted the US-backed peace plan, known as the roadmap.
This calls for an end both to the intifada and to Israeli settlement activity, leading to Palestinian statehood by 2005.
Hamas - which has spearheaded suicide bombings and other attacks in the 32-month-old intifada - does not recognise Israel and rejects the roadmap.