Two Palestinian teenagers were killed in an airstrike in Gaza City, while three Israelis were wounded from a rocket that landed on a residential home.READ MORE: Syria says it thwarted an Israeli missile attack on Homs air baseIsrael said it was focused on hitting militant targets and was warning Gaza civilians to keep their distance from certain sites. But even before the report of casualties the intense tit-for-tat airstrikes and rocket barrages still marked a significant flare-up after a long period of a generally low-level, simmering conflict.WATCH: Plumes of smoke rise after Israeli strike in Gaza City
Click to play video: 'Plumes of smoke rise after Israeli strike in Gaza City'
Plumes of smoke rise after Israeli strike in Gaza City
“The Israeli army delivered its most painful strike against Hamas since the 2014 war and we will increase the strength of our attacks as much as necessary,” Prime Minister Benjamin Netanyahu said.Lt. Col. Jonathan Conricus said the latest Israeli sortie, the third of the day, struck some 40 Hamas targets including tunnels, logistical centers and a Hamas battalion headquarters. He said the escalation was the result of the sustained Hamas rocket attacks, its fomenting of violence along the border and its campaign of launching incendiary kites and balloons that have devastated Israeli farmlands and nature reserves.READ MORE: Israeli forces arrest Toronto student protesting demolition of village in West Bank“Our message to Hamas is that we can and will enhance the intensity of our effort if needed,” he said. “What Hamas is doing is pushing them ever closer to the edge of the abyss … Hamas will have to understand that there is a price to be paid.”Later, witnesses reported that Israeli warplanes dropped four bombs on an unfinished building near a Hamas police and security compound in Gaza City, reducing the old structure to rubble. The four-story building is adjacent to a public park. Gaza’s Health ministry said two teenagers were killed in the strike and ten others injured.It marked the first casualties of the day. Striking in the heart of Gaza City is typically only seen during full-blown conflicts like the 2014 war and could signal that a further escalation may be in store.The Israeli military had no immediate reaction to that strike but said it had targeted a separate high-rise building in the northern Gaza Strip that was used as a Hamas urban warfare training facility. It said a tunnel was dug under the building.