Israeli troops backed by armour entered the Gaza Strip on Thursday, drawing mortar fire from Palestinian militants, witnesses said, without immediately reporting any casualties.
The incursion, east of the southern Gaza city of Khan Yunis, came as Middle East peace talks faltered with the resignation of the entire Palestinian negotiating team in protest against continued Israeli settlement building.
"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.
An army spokeswoman was unable to confirm the Israeli incursion, but said "a mortar round hit Israel near the Gaza border fence. There were no casualties or damage."
Palestinian militant group Islamic Jihad said its fighters responded to the incursion with mortar fire.
Rival Islamist group Hamas, which runs the territory's administration, then detained two of the fighters and held them for several 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.