The Israeli army's death toll in Gaza is already almost twice as high as during a ground offensive in 2014, a reflection of how far it has pushed into the enclave and of Hamas' effective use of guerrilla tactics and an expanded arsenal.
Israeli military experts, an Israeli commander and a Hamas source described how the Palestinian group has used a big weapons stockpile, its knowledge of the terrain and a vast tunnel network to turn Gaza's streets into a deadly maze.
At their disposal they have arms ranging from drones rigged with grenades to anti-tank weapons with powerful twin charges.
Israel's military said on Sunday that 121 soldiers had been killed since the ground campaign began on Oct. 27, when tanks and infantry began to push into Gaza's cities and refugee camps.
That compares with 66 in the 2014 conflict, when Israel launched a more limited three-week ground incursion but the goal then was not to eliminate Hamas.
"There is no comparing the scope of this war to 2014, when our forces mostly operated no deeper than a kilometre inside Gaza," said Yaacov Amidror, a retired Israeli major-general and former national security adviser who is now at the Jewish Institute for National Security of America (JINSA).
He said the army "has yet to find a good solution for the tunnels," a network hugely expanded in the past decade.
Israel's offensive was launched after the Oct. 7 rampage by Hamas gunmen who Israel said killed 1,200 people and took more than 200 hostage - some of them now freed.
Since the war began, close to 19,000 people have been killed in Gaza, sparking international demands for a ceasefire and even calls from Israel's staunch ally the United States for a shift in strategy and more precise strikes.
Prime Minister Benjamin Netanyahu said on Thursday Israel would wage war "until absolute victory". Israeli officials have said it could take months before being complete.
"It has been a challenge from day one," Ophir Falk, foreign policy adviser to Netanyahu, told Reuters, saying the offensive had come with a "huge price" in Israeli soldiers.
"We know that we're going to probably have to pay an additional price to complete the mission."
HEAVY FIGHTING
Hamas has posted videos on its Telegram channel this month showing fighters with bodycams weaving through buildings to launch shoulder-held rockets at armoured vehicles. One of them, posted on Dec. 7, was from Shejaiya, east of Gaza City, an area where both sides reported heavy fighting.
In another post on Dec. 5, a camera emerges from a tunnel, like a periscope, to scan an Israeli camp where soldiers rested. The post said it was later hit by an underground blast.
Reuters could not verify the videos.
A Hamas source, who spoke to Reuters from inside Gaza on condition of anonymity, said fighters moved as close as possible to launch ambushes "taking advantage of the land we know like no others do", often moving around or emerging from tunnels.
"There is a huge discrepancy between our power and their power, we don't fool ourselves," he said.
Hamas has not said how many of its fighters have been killed. Israel's military has said it has killed at least 7,000. The group has previously dismissed the Israeli figure, saying it includes civilians.
Hamas spokespeople outside Gaza did not immediately respond to Reuters requests for comment on this article.
An Israeli commander, who fought in 2014, said the expanded scope of this operation meant more troops were on the ground, giving Hamas the "defender's advantages", so higher troop casualties were to be expected. He asked not to be named because he is an active reservist in this war.
Israel's military does not release numbers of troops involved or other operational details.
Israel's Channel 12 television showed one army reservist unit, wary of booby-trapped doors, smashing through the wall of a building to enter a room to discover a munitions cache.
Mirroring tactics used in 2014, Israel's military has posted images on social media showing routes smashed through built-up areas by bulldozers so troops can avoid existing roads that might have landmines.
Even in some districts in north Gaza where many buildings have been pounded into rubble, bouts of fierce fighting have persisted.
BUILDING UP FORCES
"Hamas made some huge steps to build up its force since 2014," said Eyal Pinko, a former senior official with Israel's intelligence services who is now at Bar Ilan University's Begin-Sadat Center for Strategic Studies.
He said some advanced arms, such as Russian-designed Kornet anti-tank missiles, were smuggled in with the help of Hamas' ally Iran. But he said Hamas had mastered building other weapons in Gaza, such as RPG-7 rocket-propelled grenades, and the militants now had a bigger munitions reserve.
Hamas posts have said the group's weaponry includes "tandem" anti-tank weapons with two charges to pierce armour, which Pinko also said was in the militants' arsenal.
Hamas videos often show big blasts when vehicles are hit. Israeli military experts a blast did not mean a vehicle was destroyed as they said it could also be caused by defensive systems that exploded to halt incoming projectiles.
Ashraf Abouelhoul, the managing editor of Egypt's Al-Ahram daily who previously worked in Gaza and is a specialist on Palestinian affairs, said militants moved as close as possible to launch missiles and "locally-made projectiles".
But he said Israeli drones and other tactics were eroding their ability to surprise, even in urban areas. "City fighting has become more difficult" for the militants, he said.
Israel's military posted a video this month that it said showed militants emerging from a tunnel under a bombed building, before both were struck by missiles.
"Hamas may post their new weapons and tactics, (but) in principle, it remains a guerrilla resistance movement," said Alexander Grinberg, a former Israeli military intelligence officer with the Jerusalem Institute for Strategy and Security.
