Major Avital Leibovich, an Israeli military spokeswoman, told Al Jazeera that "a few reserve units have entered Gaza to participate in the operation" but would not say how many soldiers were involved.
"We are not talking about a massive amount of forces, rather a limited one," Leibovich said.
Al Jazeera's Alan Fisher, reporting from the Israel-Gaza border, said the move appeared to be in preparation for the so-called third stage of Israel's offensive: moving troops into the towns and cities of Gaza to fight door-to-door.
The deployment came amid some of the most intense fighting since the ground offensive began on January 3, with Palestinian fighters putting up stiff resistance to the Israeli advance into Gaza City.
Medical sources said that dozens of Palestinian fighters were killed in clashes on Sunday, taking the total number of Palestinian deaths since Israel began its war to 890, about a quarter of them children.
Almost 4,100 Palestinians have also been wounded since the beginning of the offensive.
Egyptian authorities had allowed 61 Arab doctors to enter the Gaza Strip via the Rafah crossing between the two nations on Monday morning.
Thirteen Israelis have been killed since the military offensive began, including three civilians hit by rockets fired from the Gaza Strip into Israel.
Al Jazeera's Ayman Mohyeldin, reporting from Gaza City, said that Israeli manoeuvres had raised speculation that a full attack on targets in the city was being planned.
|Israel has failed to achieve its stated aim of stopping rocket fire from Gaza [Reuters]
Tanks were positioned on the edge of the city to the north and east, while a column of tanks to the south advanced only to later pull back.
And as its troops pushed farther into the north, air raids in the south were pummelling the Rafah area near the border with Egypt, where there are believed to be a series of underground tunnels.
Olmert told an Israeli cabinet meeting on Sunday that "Israel is getting close to achieving the goals it set for itself".
He told ministers that Israel had "dealt Hamas an unprecedented blow... It will never be the same Hamas", according to Oved Yehezkel, the Israeli cabinet secretary.
But the Israeli military onslaught has, so far, failed to achieve the stated aim of stopping Palestinian fighters from firing rockets into southern Israel.
About 20 rockets were fired across the border on Sunday, but failed to cause any casualties.
Israel says this is far fewer rockets than were being fired daily before it started its Gaza offensive.
'Third stage' debate
The Israeli cabinet meeting had been expected to include discussion of a possible "third stage" of the offensive in which the military would enter Gaza's urban areas.
|Israeli citizens in Ashkelon shelter from rockets fired from the Gaza Strip [AFP]
However, several Israeli officials suggested that the offensive could be drawing to a close after last week's UN Security Council resolution calling for an immediate ceasefire.
"The decision of the security council doesn't give us much leeway," Matan Vilnai, the deputy defence minister, told public radio.
"Thus it would seem that we are close to ending the ground operation and ending the operation altogether."
Giroa Eiland, a former Israeli national security adviser, told Al Jazeera that there was a debate within the Israeli government and security establishment about what the goals of the operation should be at this stage.
"The main question is how to conclude and accomplish the missions," he said.
"As far as I can understand one of the reasons the military option might be expanded is in order to give an Israeli solution to the situation."
Amos Gilad, a senior Israeli official, was expected to travel to Cairo in the coming days to discuss a plan to end the fighting after Hamas officials met Egyptian officials on Sunday.