JERUSALEM (AFP) - Israeli warplanes hit Gaza on Tuesday after Prime Minister Ehud Olmert threatened "the severest riposte" to a military grade Grad rocket fired by Palestinian fighters into a southern town. The rocket attack overshadowed Egyptian-brokered talks aimed at consolidating the unilateral ceasefires declared by Israel and Hamas. Witnesses said Israeli warplanes bombed smuggling tunnels on Gaza's border, while Defence Minister Ehud Barak confirmed late afternoon that air operations were under way in the embattled coastal strip. "I suggest Hamas doesn't fool around with us," Barak told a security conference in Herzliya, north of Tel Aviv. "The air force is operating in Gaza as we speak. We promised calm in the south and we will keep our promise." "Any provocation, even the slightest, will trigger the severest riposte until this fire comes to a complete end," Olmert told reporters, just hours before the air raids began. Tuesday's rocket struck the Israeli port city of Ashkelon causing damage but no casualties, medics said. "We have to react hard to this fire," Livni told army radio. In Cairo, a Hamas delegation was meeting Egyptian intelligence chief Omar Suleiman and expected to give its response to a proposal for a long-term truce around Gaza.