Hamas warned Israel it would face a military escalation on Wednesday after its warplanes bombed the Gaza Strip following rocket fire from the Palestinian territory.
"The occupation (Israel) will pay the price for any aggression against our people or resistance sites and the response will be direct," said the militant group, which rules Gaza.
"We will increase and expand our response to the extent that the occupation persists in its aggression," the group added in a statement
Israel bombed sites in the Gaza Strip early on Wednesday, Palestinian security sources said, after rocket fire from the Hamas-controlled territory into Israel the previous evening.
Witnesses told Reuters that a training base run by the Hamas militant group, which controls Gaza, was hit in the air strike on Wednesday.
Hours earlier, a rocket fired by Palestinian militants in Gaza struck the coastal Israeli city of Ashdod, wounding two people. The Israeli military said rocket-warning sirens went off in Israeli communities bordering Gaza after the two rockets were fired from the Gaza Strip, one of which was intercepted by its Iron Dome anti-missile system.
There was no immediate claim of responsibility from Palestinian factions operating in Gaza.
That latest rocket fire came after a month in which militants in the strip had stepped up incendiary balloon attacks against Israel, which responded with nighttime air strikes against Hamas.
But the two sides at the end of August reached a deal to end hostilities and revive a fragile 18-month truce.
Hamas has ruled Gaza since 2007, when it seized power from the internationally backed Palestinian Authority.
A number of Palestinian militant groups operate in Gaza, but Israel holds Hamas responsible for attacks and typically responds to rocket fire with air strikes on militant targets.
Israel and Hamas have fought three wars and engaged in several smaller skirmishes since 2007.