• Optics and throwing off the enemy are key reasons for the ambiguity in what appear so far to be smaller land operations, rather than a full-scale ground invasion, analysts say.
• The expanded ground attacks follow more than three weeks of heavy aerial bombardment by the Israeli Defense Forces of the densely populated Gaza Strip.
• While the IDF's focus is on the northern part of the Gaza enclosure, which it says is a Hamas stronghold, the military is attacking "all parts" of the territory, an IDF spokesperson said.

Israel's military is expanding its operations in the Gaza Strip, but has avoided calling it a "ground invasion" despite sending tanks into the territory. That's by design, security analysts say.

Saturday marked the start of the "second stage" of Israel's war against Hamas, with Israeli Prime Minister Benjamin Netanyahu warning that the fight will be "long and difficult," amid rising risks of a wider Middle East conflict.

A key reason for the ambiguity in what appear to be smaller land operations, rather than a full-scale land assault, is to throw off the enemy, analysts say.

"They seem to want to keep Hamas guessing if this is really it or just a short, sharp strike op," a former British army intelligence officer, who spoke anonymously due to professional restrictions, told CNBC.

Another reason is optics. Israeli strategists are wary of triggering a major response from its enemies Iran and Hezbollah, the well-armed Iranian-backed militant organization in Lebanon on Israel's northern border, says Ryan Bohl, a senior Middle East and North Africa analyst at Rane.

"The biggest reason they won't call it an 'invasion' is PR and optics, as they aren't trying to create a political incentive for Hezbollah and Iran to escalate and they don't want the negative international attention from such a massed assault," Bohl said.

An invasion would also imply the IDF wants to permanently occupy captured land, which top Israeli officials have expressly opposed, given the high cost and danger to Israeli troops of a military re-occupation of the Gaza Strip.

The expanded ground attacks follow more than three weeks of heavy aerial bombardment by the Israeli Defense Forces of the densely populated Gaza Strip, home to over 2 million Palestinians who have lived under an Israeli blockade since 2007. The IDF says a ground offensive is the only way to ensure the destruction of Hamas' intricate network of underground tunnels, adding that it is only targeting Hamas positions in its campaign.

The Israeli bombings came in response to an unprecedented terrorist attack by Palestinian militant group Hamas on Oct. 7 in southern Israel, which killed more than 1,300 people in Israel and saw more than 240 civilians and military personnel taken hostage into Gaza, the IDF says. Israel's military response has killed more than 8,500 people in Gaza, Palestinian authorities say.

CNBC could not independently verify either set of figures.

Shortly after the Oct. 7 Hamas attack, Israel's government ordered a complete siege of Gaza, cutting off all water, food and electricity supplies to its population, which the United Nations has condemned as illegal under international law, raising the alarm over a catastrophic humanitarian crisis. The U.N. has similarly denounced Hamas for its mass killings and hostage-taking, also illegal under international law.  

Attacking 'all parts' of Gaza

While the IDF's focus is on the northern part of the Gaza enclosure, which it says is a Hamas stronghold, the military is attacking "all parts" of the territory, IDF spokesperson Jonathan Conricus said Tuesday. He noted that "additional forces" have entered the strip, which is roughly the size of the city of Philadelphia, while stressing that the IDF will not disclose the exact locations of its troops.

On Oct. 13, the Israeli military told the 1.1 million residents of the northern half of the Gaza Strip to evacuate southward in preparation for the offensive, although bombing in the south continues.

"We will focus our activities in the northern part of Gaza, that is the center of gravity of Hamas ... but we are also continuing to strike in other parts of Gaza," Conricus said. "We are hunting their commanders, we are attacking their infrastructure," he said, noting that Israel had sent heavily armored vehicles, tanks and bulldozers into the strip.

The IDF is simultaneously engaged in combat with Lebanese militant group Hezbollah, with whom it has traded fire since the early days of its conflict against Hamas.

"What is important here is for the state of Lebanon to understand that they stand to lose almost everything and gain absolutely nothing by allowing Hezbollah to drag them into a war," Conricus said Tuesday.

Another major challenge for Israel lies in combatting an enemy that likely anticipated and has prepared for a heavy ground invasion, says Hussein Ibish, a senior resident scholar at the Arab Gulf States Institute in Washington.

"Why is Israel being so secretive? Because they are fighting an enemy that has outwitted them on Oct. 7 and has undoubtedly prepared a response to Israeli ground incursions into the urban centers of Gaza that will be surprising, nasty and difficult to cope with for the Israeli troops," Ibish said.

"Uncertainty is one reason for the secrecy. Efforts to rescue hostages is another reason. That could be compromised by too much information ... There's also probably an effort involved in trying to manage international and Israeli public opinion, from very different angles."

Israel has tactical considerations, too: a massed offensive would result in heavy military, as well as civilian casualties, "neither of which serves Israel's overall strategy," Bohl said.

The IDF "can use its overwhelming numbers, control of the air, and superior intelligence to deploy force in tactically superior locations to squeeze Hamas, isolate groups of them, and wipe them out with fewer risks to civilians and soldiers."

The IDF did not immediately respond to a CNBC request for comment.

It also reduces the risk that Hamas executes hostages en masse, Bohl added, if the militants believe they can still negotiate pauses in fighting or withdrawals. A Hamas official has previously said that hostages can only be released in the event of a cease-fire, although four hostages have been released so far.

Cease-fire calls rejected

Residents of Gaza have described to CNBC their terror at being trapped inside sealed borders as more buildings are leveled and drinkable water runs out. The WHO warns that Gaza's hospitals are collapsing, as they run out of fuel and medicine, and aid groups say the several dozen aid trucks that have been able to enter the strip are not nearly sufficient to meet Gaza's humanitarian needs.

The U.N. General Assembly on Oct. 27 adopted a resolution calling for an "immediate, durable and sustained humanitarian truce" between Israeli forces and Hamas militants in Gaza, with 120 countries voting in favor and 14 against. The latter group included Israel and its long-term ally, the U.S.

Israel's Foreign Minister Eli Cohen called the resolution, which was non-binding, "despicable."

The U.N. classifies Israel as an occupier state over the Palestinian territories and says the occupations and annexations following the 1967 Six-Day War remain in violation of international law. The U.N. Human Rights Office has urged both Israel and Hamas to respect international law, calling repeatedly for a humanitarian ceasefire.