Israeli helicopters fired three missiles into the northern Gaza Strip early on Saturday injuring three Palestinians militants, witnesses said.
"The helicopters opened fire after suspect movements near the security barrier (between Israel and the Gaza Strip) to the east of Jabaliya" refugee camp, said an Israeli army spokesman.
The rockets injured armed militants from Islamic Jihad and the Popular Resistance Committees, witnesses said.
Israeli tanks also moved several metres into the Gaza Strip, the witnesses said.
On Wednesday Israeli troops entered the Gaza Strip in the first incursion since a November ceasefire, killing one Palestinian militant.
Israel withdrew all troops from the Gaza Strip in November as part of a ceasefire after six months of military operations aimed unsuccessfully at freeing captured soldier Gilad Shalit and halting the rocket fire.
But some militant groups have refused to abide by the ceasefire deal and have since fired 155 rockets at Israel, according to the army. In December rocket fire wounded two teenagers in the Israeli community of Sderot.
On March 28, Israel launched its first strike against a militant rocket team in the northern Gaza Strip since the November ceasefire, but no soldiers entered Gaza during that strike.