Israel says its fighter jets have hit dozens of Palestinian militant targets overnight in Gaza after militants fired 370 rockets at Israel.
At least three Palestinians died in the strikes on Gaza, while a civilian was killed in a rocket attack in the Israeli town of Ashkelon.
Both Israel and Hamas, which rules the Gaza Strip, have threatened to escalate their actions.
Violence erupted when a covert Israeli mission got exposed in Gaza on Sunday.
Seven Palestinian militants, including a Hamas military commander, were killed during the incident, including a member of the Israeli undercover unit
Read more about the effects of this upsurge here.