UN Secretary General Ban Ki-moon has called for restraint from all sides after escalating violence in the Gaza Strip and Israel.
The Israeli military bombed 29 places in the besieged Palestinian territory, after at least 60 rockets were fired into southern Israel on Wednesday.
The rocket fire, which Israeli police said resulted in no casualties, was claimed by the Islamic Jihad group and came a day after Israel killed three of its members in a Gaza air strike.
"The Secretary-General strongly condemns the multiple rocket attacks today on Israel from Gaza, for which Islamic Jihad has claimed responsibility," Ban's press office said in a statement.
"While reports of damage and injuries are still being ascertained, (Ban) deplores the severe escalation of violence," it said.
"He urges all actors to exercise maximum restraint to prevent further incidents that could bring greater escalation and destabilisation in the region."
Islamic Jihad's armed wing, the Al-Quds Brigades, issued a statement claiming to have fired "70 rockets" at Israel.
The Al-Quds Brigades further said its bombardment would continue in response to Israel's "aggression".
Hamas warned Israel against escalating the confrontation.
"We hold the occupation responsible, we warn of the consequences of any escalation and we reiterate that resistance is the right of the Palestinian people to defend itself," Ihab al-Ghassin, a spokesman for Hamas, said.