Israel is preparing for a ground invasion of Gaza. Here's why it hasn't happened yet.

• Israel said it would launch a ground invasion of Gaza after the October 7 terrorist attacks.
• But three weeks on, no such invasion has happened.

Shortly after the Hamas terrorist attacks on October 7, Israel announced that it would launch a ground invasion of Gaza.

Prime Minister Benjamin Netanyahu ordered the "complete siege" of Gaza, which is home to around two million people. He called up more than 350,000 Israeli reservists and ordered the immediate bombing of military and civilian targets in Gaza, killing more than 5,000 people, according to the United Nations.

But three weeks on, little has happened. Here are some of the reasons why Israel could be delaying its ground offensive.

Securing the release of Israeli captives

Hamas militants took more than 200 people hostage during the October 7 terrorist attacks on southern Israel, which killed more than 1,400 Israelis and injured over 5,400.

While some hostages have been released, the majority are thought to be kept in a vast network of underground tunnels in Gaza, according to one 85-year-old Israeli captive who was freed this week.

Due to the number of hostages, President Joe Biden's administration advised Israel to delay its much-anticipated ground invasion to allow more time for negotiations and humanitarian aid deliveries into the region, The New York Times reported.

In a phone call on Sunday, Biden and Netanyahu both "discussed ongoing efforts to secure the release of all the remaining hostages taken by Hamas — including US citizens — and to provide for safe passage for US citizens and other civilians in Gaza who wish to depart," the White House said in a statement, as per The Times.

"If Washington thinks they have the ability to squeeze more hostages out in advance of a ground invasion by working with Egypt and Qatar, they will seek to do that," Jonathan Lord, a senior fellow and the director of the Middle East Security program at the Center for New American Security in Washington told NBC News.

While negotiations have been slow-moving, Israel is still trying to get back as many hostages as possible. On Wednesday, its military dropped thousands of leaflets into Gaza, asking Palestinians to reveal information on hostages' whereabouts, in exchange for money and protection, Sky News reported.

US military action

US officials, including Defense Secretary Lloyd J. Austin III, have also urged Israel to halt their offensive in an effort to advise it on its military actions and discuss American arms shipments, the Times reported.

"We have a close dialogue and consultations with the US administration. The US is not pressing Israel in regards to the ground operation," a diplomat from the Israeli Embassy in Washington told the Times.

US military officials are making their own preparations, scrambling to deploy nearly a dozen air defense systems in the region, The Wall Street Journal reported on Thursday.

The US military and other officials believe their forces will be targeted by militant groups once Israel launches its ground invasion, according to the report.

Preparations for a possible wider regional war

Meanwhile, allies of Israel are conscious of the ongoing tensions with Hezbollah, an Iran-backed militia group, that could attack Israeli forces from Lebanon and open a northern front.

"Nobody has an appetite for two fronts at this point," one US official told NBC News.

Other militias are also active in Syria, Iraq, and Yemen.

US officials believe that once the ground invasion begins, American forces will be targeted by various militant groups, the Wall Street Journal reported.

Political pressure

Netanyahu, who is already on unstable political ground after the terrorist attack, still needs to make some major decisions before a ground offensive, according to reports.

For example, a senior official told NBC News that the prime minister has not yet settled on an exit plan for how and when Israeli ground forces will leave Gaza.

This is partly because military meetings have so far focused only on day-to-day operations as Israel continues to bomb Gaza.

On top of this, Netanyahu and Israel Defense Forces (IDF) officials have come under intense scrutiny for the intelligence and policy failures that allowed Hamas to carry out its deadly attacks.

Therefore, Israeli leaders need to be extra diligent about their next steps, to make sure they not only please their allies but also their country.

"Almost everyone making decisions on this knows they bear some responsibility for the disaster of October 7, whether that's the political leadership or the military and security leadership," Robert Satloff, the Howard P Berkowitz chair in US Middle East policy at the Washington Institute for Near East Studies told NBC News.

"They all know that how Israel performs in this next phase is their last chance to write what may be their final chapter in public life," he added.

It is unclear when the ground offensive will really begin. Netanyahu has not given a timeframe, and said Thursday that he would not provide any details to "secure the lives of our soldiers."

The timing of the IDF operation will be "unanimously" determined by Israel's war cabinet, he added.