Palestinian militant groups have pledged to continue their armed campaign against Israel, rejecting moves by the Palestinian Authority towards peace with Israel.
Hamas - incensed at Abu Mazen's 'concessions'
After a meeting in Gaza on Saturday, the groups endorsed a decision by Hamas to break off ceasefire talks with Palestinian Prime Minister Mahmoud Abbas - widely known as Abu Mazen.
The suspension followed Abu Mazen's promise to end the intifada at this week's Middle East summit in Aqaba in Jordan.
Early on Sunday at least three Palestinians opened fire at the Erez checkpoint, the main crossing point between the Gaza Strip and Israel, according to Israeli public radio.
They injured at least six people before being shot by Israeli troops, the radio said.
The BBC's Barbara Plett says Saturday's announcement by the militants undermines the prime minister's strategy to secure a ceasefire from all Palestinian groups.
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 Abu Mazen's own Fatah movement.
"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.
A Hamas spokesman said his group would only resume the ceasefire talks 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's (R) call for peace with Israel is supported by the US
Abu Mazen has accepted the US-backed peace plan known as the roadmap.
The plan calls for an end to both the intifada and 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.
On Friday the group broke off talks about a ceasefire with Israel, because of Abu Mazen's conciliatory stance at Aqaba.
Even before the Saturday meeting, moderates within the Palestinian Authority condemned the move and said Abu Mazen would not meet Hamas as a result.
A Palestinian official told Reuters news agency that Hamas's walkout was "irresponsible" and "indicated that they are not interested in cementing the national unity of the Palestinian people".
However, the Palestinian Authority also made it clear that it will not use force against the radical groups.
Israel has insisted that attacks by militants must stop if the renewed peace process is to move forward.
There was more violence in Palestinian areas on Saturday.
An armed Palestinian was shot dead by an Israeli army patrol in the Gaza Strip, an Israeli military source said.
Meanwhile the Israeli army has sealed off the West Bank - preventing Palestinians from crossing into Israel.
Military officials said the measure followed "heightened and numerous terror alerts".
Israel lifted its last closure a week ago, after a meeting between Abu Mazen and Mr Sharon.