The length and intensity of the escalation could be determined in part by whether Hamas joins Islamic Jihad in returning fire.
In the past, Hamas has occasionally sat on the sidelines as Islamic Jihad clashed with Israel, and the group did not immediately rule out repeating that approach on Friday.
“As we mourn the leader al-Jabari and the righteous martyrs, we affirm that matters are open to all directions, calling for an end to the Zionist aggression against our people,” Ismail Haniyeh, chief of Hamas’s political bureau, said in a statement.
U.N. officials were attempting late on Friday to persuade all sides to stand down.
In the aftermath of the initial strikes, plumes of smoke billowed over the Gazan skyline. On the ground, throngs of rescuers, medics and onlookers gathered in the street near where the Islamic Jihad commander had been killed. Photographs posted online showed him being carried through a crowd, and a grieving man carrying what appeared to be a dead child covered in a shroud.
The airstrikes moved the focus of conflict back to Gaza after a period of heightened violence in Israel and the West Bank.