Gaza tunnels are a vast network of tunnels which Hamas claimed they have used to infiltrate. According to KTVU, the Israel Defense Forces has decided on making a top priority the destruction of the Gaza tunnels a top priority, even releasing a video of soldiers setting off explosives at the entrances of the Gaza tunnels.

In response to the IDF's move, Hamas released its own video via several media outlets. The video reportedly showcased Hamas fighters moving about the tunnels beneath the Gaza Strip.

On Saturday, the militants wearing Israeli army uniforms made their way across the border by sneaking in through the Gaza tunnels. The militants killed two Israeli soldiers in the process.

According to The Wall Street Journal, the sneak attacj was "the worst blow to the Israeli military on its side of the Gaza border in years."

According to KTVU, the Gaza tunnels provide Hamas a great advantage, and now Israel fears the Gaza tunnels  may be used to infiltrate Israel itself and ambush their civilians or soldiers.

NBC reports that the Gaza tunnels can be extremely sophisticated, as 'Some boast concrete walls and ceilings, electric lighting, radio communications, sub-tunnels running off to the sides, and many are replete with booby-traps in case Israeli forces enter them.'

The Palestinian militant group has reportedly been expanding its network of tunnels, including the Gaza tunnels, for years.

According The New York Times, one Israeli military official even said that there are actually 'two Gazas ... One above ground and another under the ground.'

Al Jazeera reported that the Gaza tunnels made headlines in 2006 when Hamas used one of them to cross the border to capture an Israeli soldier. They held the soldier prisoner for five years and was later released in exchange for 1,000 jailed Palestinians.

In 2013, Euronews said that when Israel discovered the Gaza tunnels, their military froze imports of all building materials to Gaza.

KTVU said similar cross-border tunnels have also been used to smuggle goods from Egypt. However, most have been shut down by Egypt's new government as part of its crackdown on the Muslim Brotherhood, of which Hamas is considered an offshoot.  

According to reports, it is only Gaza residents often suffer most from the closure of Gaza tunnels. A Vox report said, 'Civilians have a hard time accessing basic supplies, like medicines and construction material. The Gaza economy is stifled, and unemployment is estimated to be over 40 percent. The tunnels are the means Gazan civilians have to deal with it. Between Israel and Egypt, they may be in rough shape.'

Meanwhile, Israel has reportedly extended its ground offensive. According to a hospital spokesperson in Gaza as told to CNN, a shooting by an Israeli in a town near Gaza City on Sunday killed at least 40 and wounded 300 others.

The New York Times reports that the Israeli military has avoided two more access into its territory via the Gaza tunnels on Monday morning. They have also killed 10 militants in the process.

Gaza tunnels used Sunday which killed at least 40 was the latest incursion to have unfolded and established before the state of Israel.