Israeli warplanes bombed two separate targets in the Gaza Strip on Thursday after Palestinian militants fired projectiles across the border, the army said.
The strikes in northern Gaza came just hours after witnesses reported an Israeli army incursion inside the Strip's eastern borders, which Islamist militants claimed to have responded to with mortar fire.
The Israel Defence Forces said "aircraft targeted two concealed rocket launchers in the northern Gaza Strip" in response to two projectiles that had hit Israel since Wednesday.
An army spokeswoman told AFP one of the projectiles was a rocket, and the other was a mortar shell.
"Launching rockets against Israel and its civilians is a breach of our sovereignty. We maintain the right to operate against those who are involved in terror," said army spokesman Lieutenant Colonel Peter Lerner.
No casualties were reported in any of the attacks from either side.
Witnesses said earlier that Israeli troops backed by armour entered Gaza east of the southern town of Khan Yunis.
"Six military bulldozers accompanied by several tanks entered about 200 metres (yards) from the border into farmland, as helicopters and spy planes circled above near the village of Khuzaa," one witness told AFP.
"Resistance fighters fired several mortar rounds at the Israeli forces and explosions were heard in the area," the witness added.
Palestinian militant group Islamic Jihad said its fighters responded to the incursion with "four mortar shells", but made no mention of rocket fire, and did not specify where the shells had landed.
Rival Islamist group Hamas, which runs the territory's administration, detained two of the fighters and held them for hours before releasing them, an Islamic Jihad spokesman said.
Hamas has endeavoured to enforce a year-old Egyptian-brokered truce with Israel which ended the last major outbreak of fighting in and around Gaza late last year.
But on November 1, four Hamas fighters were killed and five Israeli soldiers wounded in an exchange of fire.
The casualties came during an incursion into the territory by the Israeli army to destroy a tunnel under the border it alleged was intended as a springboard for attacks inside the Jewish state.
The exchanges of fire came as Middle East peace talks faltered with the resignation of the entire Palestinian negotiating team in protest against continued Israeli settlement building.