A Hamas leader in Gaza city said on Thursday that the rocket fire against Israeli towns is an act of self defense.
Hamas leader Sami Abu Zuhri warned that the agreement with Israel to maintain calm does not mean to "surrender."
"The Israeli occupation is fully responsible for the escalation taking place. This escalation started off with the execution of three members of the Islamic Jihad and we assure you that the Palestinian resistance is defending itself when confronting these crimes," Zurhi said.
Zuhri continued: "We affirm that Hamas and the resistance will never allow the occupation to create a new reality at the expense of the Palestinian resistance or changing the agreement for calm into an agreement for surrender."
Palestinians in the Gaza Strip fired rockets at Israeli cities on Thursday, police said, in a second day of a cross-border flare-up.
Sirens sounded in the southern Israeli towns of Ashkelon and Ashdod. Police said the rockets had landed in open areas, causing no casualties.
The Israeli military carried out 29 air strikes and fired tank shells at militant targets in the Gaza Strip on Wednesday after the Islamic Jihad group launched 60 rockets toward Israel in the heaviest barrage in nearly two years.
No casualties were reported on either side of the frontier in Wednesday's incidents. Islamic Jihad said its rocket fire had been a response to Israel's killing of three of its men a day earlier.