A former deputy Israeli military chief of staff described the possibility that troops would enter Hamas's significant tunnel infrastructure as a "grave mistake."

Hamas has used significant time and resources to build a web of tunnels underneath densely populated areas in Gaza that has allowed it to smuggle weapons, stockpile supplies and fuel for this current conflict, and avoid Israeli airstrikes.

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“The wisdom is to find the entrances and seal them, or send in smoke that will cause the enemy to come out or will harm him,” Yair Golan told Army Radio, according to the Times of Israel. “Under no circumstances do you fight in the tunnels … where there is no chance that you won’t get hurt. You don’t fight inside the tunnels; you counter the threat of the tunnels."

In 2021, Hamas claimed to have built more than 300 miles of tunnels, which they were able to build, according to Israeli officials, by diverting humanitarian aid to the construction of the tunnels.

Israel Defense Forces spokesman Rear Adm. Daniel Hagari said on Thursday that "troops completed the encirclement of Gaza City, which is the focal point of the Hamas terror organization."

As the troops moved to encircle Gaza City, they encountered booby traps and minefields.

“This is certainly terrain that is more heavily sown than in the past with minefields and booby traps,” Brig. Gen. Iddo Mizrahi, chief of Israel’s military engineers, told Army Radio, according to Sky News.

"Hamas has learned and prepared itself well," he added, per Reuters.

It's also believed that the more than 200 hostages, who were kidnapped during the Oct. 7 terrorist attacks, are within the labyrinth of tunnels. Only five of them have been released to date.

The tunnels have lighting, electricity, air conditioning, and in some areas rails to help transport goods, IDF spokesman Maj. Doron Spielman told the Washington Examiner last month. He called the "metro" system a "highly sophisticated underground terror web."

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Israeli forces launched a controversial airstrike on Tuesday that collapsed the tunnel infrastructure in a densely populated urban area near Jabalia. Israeli military leaders said dozens of Hamas terrorists were killed in the strike, including Ibrahim Biyari, who was a battalion commander leading operations and fighting against Israel. Buildings above ground collapsed following the collapse of the tunnels.

The strike, due to the dense population put at risk during it, led to an outpour of condemnation from other Middle Eastern countries.