The Israeli military said its forces had found five tunnels in the southern Gaza Strip used by militants to smuggle in weapons from Egypt.
Palestinian hospital staff said Israeli troops killed two gunmen from the governing Hamas in clashes in the town of Rafah.
In the northern Gaza Strip, residents said at least two Palestinians who they identified as a Hamas gunman and a civilian, were killed by Israeli forces overnight.
An Israeli army spokesman said soldiers had shot two gunmen in Rafah. He said he was unaware of any clashes between troops and militants in the northern Gaza Strip.
Residents said some tanks took up positions outside the main gate of the Rafah terminal and an army bulldozer tore up the road leading to it.
But the Israeli forces did not enter the border crossing, which has been open only sporadically since Israel renewed ground operations in the Gaza Strip in June.
Although under Palestinian control with EU monitors, Israel has effective power to shut the crossing by cutting off access roads inside Israeli territory used by the European staff.
Hamas said the deployment around the Rafah crossing -- Gaza's only link to the outside world that does not pass through Israel -- was tantamount to Israeli reoccupation of the border area. But Israel played down the scale of its objectives.
"We have no intention of going back and controlling Gaza," Defence Minister Amir Peretz told parliament. "But we are obligated to provide security for the citizens of Israel. We will not make a policy of closing our eyes to the smuggling."
GLOOM
Israel withdrew its troops and settlers from the Gaza Strip last year. Over the past week, Israel has ramped up its offensive, which it says is aimed at keeping pressure on militant groups, curtailing rocket attacks and finding cross-border tunnels.
The Israeli-Palestinian violence has deepened the gloom in the territory, which is also beset by internal clashes between factions loyal to Hamas, dedicated to destroying Israel, and to President Mahmoud Abbas, a moderate.
"We call upon the international community and the United Nations to take serious, decisive and immediate steps to block the Israeli aggression and protect civilians," the Palestinian government said in a statement.
Around 250 Palestinians, about half of them civilians, have been killed in Israel's operations in Gaza since June.
Following earlier hints that he might sack the government, Abbas said on Tuesday he had to make a decision soon on the fate of the Hamas administration.

Copyright Reuters, 2006