(NewsNation) — As Israeli forces prepare for a ground invasion of Gaza, looking to eradicate Hamas, one of the most dangerous challenges it faces may be the extensive network of underground tunnels Hamas maintains.

Hamas, which has been designated by the U.S. government as a terrorist organization, has established a network of tunnels that run underground from Gaza to Egypt and Israel since at least 2006. Samuel Katz, a counterterrorism expert and author who has written extensively about the elite special forces of Israeli’s military, described the tunnels as “a complete subterranean city known as the Gaza Metro.”

“The tunnels began as smuggling tunnels between Egypt and Raphia, the city at the southern end of the Gaza Strip, to bring in explosives, materials, money and operatives. Once the Second Intifada ended, the tunnel was expanded into a three-fold system with command and control tunnels, operational tunnels and tunnels where you can store explosives and rockets,” Katz told NewsNation host Dan Abrams.

Both Israel and Egypt have tried to dismantle the tunnels but have been met with major challenges. The pathways weave through the entire Gaza Strip and are nestled between civilian buildings, including schools and mosques.

“They go through every refugee camp, every city. Every facet of life in Gaza has been prepared for this moment,” Katz said.

From a tactical standpoint, Katz says the Israelis have special operations units that have trained for years to wage war inside such tunnels. But, he says, political pressure may be making the Israelis temporarily shy away from them.

“It’s hiding in plain sight. The elaborate tunnels are built with money and materials that were supposed to be headed for schools, hospitals, housing for the poor. All that was diverted by Hamas to build this extensive, elaborate underground city, knowing that the Israelis would want to hit the entrance and exit points, which are usually hidden inside apartment buildings, schools, mosques and hospitals, where the terrorists think that the Israelis won’t strike because of international political pressure,” Katz said.

The U.S. and others continue to warn Israel to show restraint and make sure there is humanitarian aid to Gaza. Menachem Rosensaft, an adjunct law professor at Cornell Law School who has been involved in the Middle East Peace Process for more than 35 years, says the main concern seems to be the hostages.

The Israeli military said Monday that at least 199 hostages have been taken into Gaza. Hamas claims it’s holding 200 to 250 hostages.

“I think that the basic problem here is 200 hostages. And I think that’s the main concern on everyone’s mind,” Rosensaft said. “In particular, President Biden, Secretary Blinken, they want to get those people back and they don’t want to risk killing them. So this, I think, is the reason why there’s still some degree of, shall we say, polite talk about Hamas. But let’s get something straight. Hamas is a genocidal terrorist organization.”

Along with the concern for hostages, much of the tunnels and Hamas’ military infrastructure are in residential areas. Ahead of the anticipated ground attack, Israel has issued a mass evacuation order in northern Gaza. Hamas reportedly urged people to ignore the order, and the Israeli military shared images it said showed a roadblock by Hamas to keep traffic from moving south.

Rosensaft believes Hamas is blocking people from leaving.

“I believe that they have absolutely no interest in their population, in their constituencies. They have no respect for human life of any kind. They proved that last week. They have no problem murdering people, raping women and girls, slitting the throats of infants. They are beyond any rational talking,” Rosensaft said.

Israel declared war after Hamas launched a surprise attack Oct. 7. More than 1,400 Israelis have been killed, with the vast majority being civilians left dead in the assault last weekend. At least 2,778 people have been killed and 9,700 hurt in Gaza, according to the Health Ministry there.

The Associated Press contributed to this report.