Egyptian President Hosni Mubarak spoke with President Abbas Tuesday afternoon, and told him the clashes had "crossed the line" and that both parties must cease violence immediately.
Yasser Abd Rabbo, a former minister of the Palestinian Authority, echoed such sentiments while at a convention in Petra, Jordan. He suggested "a security treaty, assuring all the militias be disarmed."
Head of the Palestinian Energy Authority Abdel Karim Abdeen warned Tuesday that power supply to Gaza might shut down, since Gaza is running out of fuel for its power plant.
"If the situation remains the same and we are not able to supply the plant with fuel, we are going to shut down by 9 AM (Wednesday), and Gaza is going to live in darkness," he told foreign news agencies.
Javier Solana, EU High Representative for the Common Foreign and Security Policy, has called both Fatah and Hamas to cease the violence and resort unity. "I am very concerned about what is happening in the Palestinian Authority," he said.
"Restoring security is vital for the continuance of the peace process with Israel."
Rising tension
More than a dozen Palestinians were killed Tuesday in clashes between Fatah and Hamas forces in the Gaza strip, when Hamas gunmen attacked a Palestinian Presidential Guard's training camp. After taking over the camp Hamas reportedly executed Fatah members of the Presidential Guard.
Hamas officials said the attack and executions came as response to the killing of Aibrahim Maniah, one of Hamas military commanders.
Armed Hamas forces later surrounded a Palestinian police center in northern Jabalia. Other Hamas armed forces had barricaded themselves inside Gaza's Islamic university, in an attempt to prevent Fatah from entering the campus.
Should the university be attacked, Hamas officials warned that Palestinian President Mahmoud Abbas' house "would not be safe." Fatah officials accused Hamas of trying to stage a military coup.
The Shifa Hospital in Gaza City reported it was struggling to deal with the numerous casualties pouring in and was in dire need of blood donations.
Meanwhile Hamas gunmen are currently laying siege to the home of Fatah leader Maher Miqdad.
Last weekend, tensions rose after armed Palestinian security forces, generally associated with Fatah, deployed in Gaza'a streets, unbeknown to Hamas.
Over the weekend an agreement was reached, calling for both parties to withdraw their troops and resume negotiations, but tensions over the security forces' deployment, set the stage for Tuesday's renewed
clashes.
Another factor, assumed to have contributed to Tuesday's clashes was Palestinian Interior Minister Hani al-Qawasmi resignation Monday, rocking the two-month-old unity government.
Roee Nahmias, AP and Reuters contributed to this article