GAZA  Palestinian militants fired a long-range rocket from Gaza into the Israeli coastal city of Ashkelon on Tuesday and Israel retaliated with airstrikes against smuggling tunnels and a Hamas outpost in southern Gaza, as Egyptian-brokered talks for a sustainable cease-fire continued in Cairo with no obvious progress.

No injuries were reported on the Palestinian or the Israeli side.

But the rocket that fell near a clinic in central Ashkelon was an imported Katyusha, the first of that more powerful type since a tenuous calm took hold more than two weeks ago. It presented a new challenge to Israeli leaders ahead of elections next Tuesday and raised the possibility of a military escalation should the Egyptian initiative fail.

“We promised peace and safety to those living in southern Israel, and we will deliver,” the Israeli defense minister, Ehud Barak, vowed Tuesday.

Israel pulled its troops out of Gaza on Jan. 18, ending a devastating three-week offensive that Israel said had been primarily meant to deter such rocket attacks. Israel and Hamas, the Islamic group that rules Gaza, declared separate cease-fires. But tit-for-tat attacks have increased since Jan. 27, when Palestinian militants detonated a bomb that killed an Israeli soldier patrolling the border.