Israeli tanks and bulldozers have entered the Rafah refugee camp in the Gaza Strip again.
Thousands lost their homes in the May operation
Palestinian sources say there have been exchanges of fire, but it is unknown whether there have been any injuries.
The Israeli army says it is looking for tunnels used for smuggling weapons into the Gaza Strip from Egypt.
At least 40 Palestinians were killed when the army last went in on an extended mission a fortnight ago,with several thousand left homeless.
The UN put the number of homeless at nearly 4,000 - a figure disputed by Israel, which said it only destroyed properties used by the militants.
The BBC's Alan Johnston in Gaza says there have been no reports of any casualties or demolitions in the latest action.
He says about 30 Israeli tanks and bulldozers have moved 150 metres into the camp, which lies close to the border with Egypt.
Earlier on Tuesday, the UN agency for Palestinian refugees said a 10-year-old boy was seriously injured by Israeli gunfire while studying at a UN school in the Rafah camp.
Mohammed Hammad received a bullet to the neck during an Arabic language class at the Al-Ummeria elementary school.
The Israeli army says it is investigating the report.
Our correspondent says the al-Ummeria school has a history of injuries and death as it is effectively built on a "frontline in the Palestinian uprising".
The Rafah camp is a power base for the Palestinian militant groups, Hamas and Islamic Jihad.
Meanwhile, Israeli Prime Minister Ariel Sharon is battling to defend his plan for a unilateral withdrawal from Gaza.
He is sending a critic of his proposals, Foreign Minister Silvan Shalom, on a visit to Egypt in what correspondents say is an attempt to win him over.
Egypt's government has offered support to Mr Sharon's plan, which envisages withdrawing Israeli troops and uprooting Jewish settlements from Gaza in exchange for greater control over larger settlements in the West Bank.
But many right-wingers and settlers within Mr Sharon's government continue to oppose the move, describing it as a betrayal of their cause and a concession to Palestinian militants.