Schools have been closed in Gaza amid what officials say is a state of anarchy caused by fighting between Palestinian factions Hamas and Fatah.
Hamas militants have been out in force patrolling Gaza City
The education ministry acted after several children were among those hurt in a day of clashes that killed three.
Violence has flared since Palestinian leader Mahmoud Abbas on Saturday called for new elections, a move the Hamas-led government branded a "coup".
Mr Abbas has called for all factions to respect a truce agreed on Sunday.
In a statement, he called on "all, without exception, to adhere to a ceasefire and to end the killings and all other operations in order to maintain our national unity".
The BBC's Nick Thorpe in Gaza says there is little sign of the ceasefire to which both sides had agreed on Sunday.
Prime Minister Ismail Haniya, of Hamas, is to deliver a speech later on Tuesday which his aides said would include an appeal for calm.
Jordan's King Abdullah has offered to host talks between Mr Haniya and Mr Abbas.
Masked Hamas gunmen set up makeshift roadblocks in Gaza City on Tuesday as gunfire echoed around the streets.
In Tuesday's violence:
- An attempt to take an injured Fatah militant to a Gaza hospital sparked a battle between Fatah intelligence officers and Hamas militiamen. One Hamas fighter was killed and several injured
- In an apparent revenge attack, the headquarters of the pro-Fatah intelligence service near Gaza City came under mortar fire
- A convoy of pro-Fatah militants was ambushed on one of the main Gaza City thoroughfares. Two Fatah militants were killed and nine bystanders injured, including five children, medical sources said.
After the children were caught up in fighting, Deputy Education Minister Muhammed Abu Shaqir described the situation as "anarchy" and cancelled all classes in the Gaza Strip.
There has been unrest since Mr Abbas - who heads Fatah - called for early elections, sparking fears of a descent into full civil war.
Palestinian MP Mustafa Barghouti, who is trying to mediate between Hamas and Fatah, said "all efforts" were being made to stop the violence.
But he added: "We could reach a point where the people in the street will stop listening to their leaders."
Gaza shopkeeper Suleiman Tuman, who witnessed some of the latest violence, told the Associated Press news agency: "I've been praying to God that this is going to end. Both sides used to fight the Israelis together. Now they are directing their weapons toward each other."
While Fatah, through Mahmoud Abbas, controls the presidency, Hamas, which won elections in January, runs the government.
9 Dec - Mr Abbas suggests early polls. Hamas denounces the idea
11 Dec - Three sons of a Fatah security chief are shot on their way to school
14 Dec - Hamas PM Ismail Haniya's convoy comes under fire as he returns from Egypt, killing a bodyguard. Hamas blames Fatah
16 Dec - Mr Abbas says he will call early elections; Hamas calls the move a "coup"
17 Dec - A truce is called following street battles between Hamas and Fatah but violence continues
Fighting between the factions has paralysed Hamas' administration, which has also been crippled by an international embargo against it.
Hamas refuses to renounce violence or recognise Israel - a crucial demand of the international community.
Fatah believes that ending anti-Israel attacks is the key to forcing Israel into negotiations on an independent Palestinian statehood.
Increased poverty and months of Israeli operations have polarised Palestinian factional rivalry further, correspondents say.
Jordan's King Abdullah said his country would do all it could "to help the Palestinians overcome their differences".
"All options are open, including a call for a meeting in Amman between [Mr Haniya and Mr Abbas]," a statement said.