"We are seeking a national unity in Palestine and we stand against the events that we have witnessed in the last days," Amr Moussa, the Arab League chief, said in the Egyptian capital.
"If you ask me Fatah and Hamas are the same: both seek power and both want to obtain it through violence"
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He said there must be an "immediate and full halt" to the violence.
Moussa said that Arab countries want to "serve the Palestinian cause, and not one faction against another".
Egypt's state MENA news agency quoted Prince Saud al-Faisal, Saudi Arabia's foreign minister, as asking the Arab League in dismay whether Palestinians had forgotten a commitment made in Mecca earlier this year to "unite and never to fight".
Meanwhile, Egypt pulled its diplomatic mission out of the coastal strip, citing security reasons.
Separately, Egyptian police said close to 100 Fatah officials crossed into Egypt from Gaza Strip in the early hours of Friday, fleeing the Hamas takeover.
Israel's military said on Friday that all crossings into the Gaza Strip had been closed "until further notice."
But the country's Channel Two TV said Israel was briefly opening the Erez crossing into Israel to enable other Fatah leaders to get out.
The Arab League backed Abbas's decision to apppoint Salam Fayyad, the World Bank economist turned Palestinian finance minister, as prime minister, saying that the "legitimacy of his leadership" must be respected.
Jordan also underlined its backing for Abbas' government.
The government rejects "any dissent or defiance to the legitimate authority" and stressed "the necessity to protect the Palestinian National Authority and its President Mahmoud Abbas", Nasser Judeh, the spokesman, said in a statement carried by the official Petra news agency.
Jordan's King Abdullah called Abbas to express sadness for the situation in Gaza and called for an immediate end to the infighting, Petra reported.