Palestinian fighters in the Gaza Strip have fired more rockets at Israeli cities in a third day of a cross-border flare-up.

Sirens sounded in the southern Israeli towns of Ashkelon and Ashdod on Thursday. Israeli police said the rockets had landed in open areas, causing no casualties.

Islamic Jihad said it has launched more than 90 rockets since Wednesday, the highest number since Israeli bombardments of the Gaza Strip in November 2012, in which more than a hundred Palestinians were killed.

The group said the latest rocket attacks were retaliation to Israel breaking a truce by killing three of its members on Tuesday.

The Israeli military carried out 29 air strikes and fired tank shells at targets in the Gaza Strip on Wednesday.

No casualties were reported on either side of the frontier in the latest incidents.

‘Maximum restraint’

United Nations Secretary General Ban Ki-moon called for restraint from all sides after the escalating violence.

"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."

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.

Source: Al Jazeera and agencies