GAZA CITY, Gaza Strip – Signaling an escalation of Israel’s Gaza operation, Prime Minister Benjamin Netanyahu told Israelis Monday to be ready for a “prolonged” war, and the military warned Palestinians in three large neighborhoods to leave their homes and head immediately for Gaza City.

The warnings came on a day of heavy fighting in which nine children were killed by an strike on a Gaza park where they were playing, according to Palestinian health officials.

Israeli tanks also resumed heavy shelling in border areas of Gaza, killing five people, including three children and a 70-year-old woman and wounding 50 in the town of Jebaliya, which was among the areas warned to evacuate, the Red Crescent said.

Many Jebaliya residents said they did not dare attempt an escape. Sufian Abed Rabbo said his extended family of 17 had taken refuge under the stairway in their home.

“God help us. We have nothing to do but pray,” the 27-year-old told The Associated Press by phone. “I don’t know who left and who stayed, but in our street, we are all very scared to move.”

Later Monday, Israeli forces fired a large numbers of flares over Gaza City.

The latest bloodshed came despite mounting international calls for a cease-fire and followed failed attempts by both sides to agree to even a lull in fighting of several hours for the start of the three-day Muslim holiday of Eid el-Fitr that marks the end of Ramadan.

The Hamas-run health ministry said 10 people, including nine children, were killed and 46 wounded in the blast at a park in the Shati refugee camp on the outskirts of Gaza City.

Israel says its troops will not leave Gaza until they have demolished scores of Hamas military tunnels under the Israel-Gaza border. Hamas says it will not cease fire until it receives international guarantees Gaza’s 7-year-old border blockade by Egypt and Israel will be lifted.