An Israeli government spokesman, Mark Regev, issued the warning after a rocket landed near the Israeli city of Ashkelon Tuesday. There were no reports of casualties.
A militant group called the Popular Front for the Liberation of Palestine has claimed responsibility for the strike.
The rocket launch follows days of quiet as an unofficial truce has taken hold in Gaza. Palestinian militants have stopped almost all of their rocket attacks against Israel.
But, during a brief visit to Ashkelon shortly before Tuesday's attack, Israeli Prime Minister Ehud Olmert cautioned that rocket fire could resume.
The lull in violence follows a recent Israeli military offensive in which at least 120 Palestinians were killed. Israel says the campaign was aimed at halting militant attacks.
According to Israeli Army Radio Monday, Mr. Olmert has ordered Israel's defense forces to stop air strikes and ground incursions into Gaza as long as Palestinian militants refrain from firing rockets at southern Israel.
Source: By VOA News
Finally they got a "hudna" they wanted
Hamas showed once again the weakness of Israel, the international community pressures us a bit and we give up. Expect a few weeks of quiet until they rearm and terrorize us again, then we retaliate, then you count the bodies and conclude it's not fair that more Palestinians died so we should just suck it up and stop responding. Until the next time.