UN Secretary General Ban Ki-moon is "extremely concerned" about the escalation of violence in the Gaza Strip and urged an extension of a recently ended truce, his office said.
"The Secretary-General is extremely concerned at statements calling into question the continuation of the Egyptian-brokered calm in and around Gaza," his press office said in a statement on Friday.
"A major escalation of violence would have grave consequences for the protection of civilians in Israel and Gaza, the welfare of the Gazan civilian population and the sustainability of political efforts."
Ban reiterated his appeal that "the calm should be respected and extended, rocket attacks against Israel must be immediately halted and all acts of violence must cease," his office said.
Shortly after the armed wing of Hamas formally announced that the six-month truce with Israel was over, the smaller Islamic Jihad group said it fired three rockets at southern Israel, which caused no reported damage or casualties.
Violence has escalated for the past several weeks in the run-up to the end of the ceasefire. Militants fired nine rockets Thursday toward southern Israel that caused no damage or victims after Israeli forces carried out five air strikes and killed one Palestinian on Wednesday.
Israel responded to violence that erupted in early November by tightening sanctions and closing its crossing points with Gaza, halting deliveries of humanitarian aid and other basic supplies.
Palestinian president Mahmud Abbas met in Washington on Friday with US President George W Bush, set to leave office on January 20 without the Middle East peace deal he had hoped to broker by the end of the year.