Four days after Israel launched a withering ground assault on the Palestinian fighters in their stronghold of Shejaia following intensive airstrikes, the Israeli army still does not have complete control of the area.

Smoke from shelled homes and the buzz of Israeli drones clog the sky above the wrecked district on Gaza's eastern border.

The thud of a buried explosive aimed at a troop carrier is met with an hour-long rain of Israeli artillery fire that shakes the width of the coastal strip, sending the deafening sound bouncing off buildings as far as the shore.

Exploiting a vast network of secret tunnels to snipe at enemy troops and blast their vehicles even inside Israel, Hamas has killed 32 Israeli soldiers -- almost three times as many as in the last major ground clashes in a 2008-9 conflict.

"The al-Qassam brigades continue to give repeated surprises, and every day the holy warriors arise from where the (Israeli) occupation could not foresee," the group said last week.

"They fight... face to face with the enemy in retaliation for the blood of the martyrs that the occupier spills daily."

The action has lived up to the fierce rhetoric.

Hamas has far outstripped fellow fighters in Islamic Jihad and other groups in sending drones, scuba commandos and tunnel raiders to take the fight into Israel.

Israeli soldiers carry the coffin of slain 20-year-old Staff Sergeant Moshe Melako who was killed the previous day during fighting with of Palestinian fighters in the Gaza Strip, on July 21, 2014.

In one such infiltration, Hamas fighters emerged wearing full Israeli uniform, but were let down by one key detail - they were carrying Kalashnikov rifles, not standard issue M16s or Tavor assault rifles.

In the most deadly incident for Israel yet, on the first day of its incursion to begin destroying the tunnels on Sunday, Hamas says its fighters watched as an enemy armored personnel carrier lurched into a web of booby traps they had laid.

"Our holy warriors detonated the minefield with such force that (the carrier) was destroyed. They advanced on it, opened its doors and finished off all left inside," the group said.

Israel offered a different account, saying the vehicle was part of a convoy and was hit my multiple anti-tank missiles.

Israel said six soldiers were killed, while another thought to have been in the vehicle is missing, believed dead. Hamas said it captured him but has not released his picture.

The Israeli military acknowledges Hamas' increased skill.

"They have undergone extensive training, they are well supplied, well motivated and disciplined. We have met a more formidable enemy on the battlefield," said Israeli military spokesman Lieutenant-Colonel Peter Lerner.

Confined in the crowded sandy coast enclave of 1.8 million, where poverty and unemployment hover around 40 percent, weary Gazans say they hope the battle will break the blockade that Israel and Egypt impose on them. They have very little to lose.

Hamas leaders hope to achieve that goal through the prowess of their men at the front, trained to inflict casualties and grab soldiers to gain political leverage.

Morale was high and Hamas fighters were preparing for a fight during a visit by Reuters in April to a training camp of its military wing on a vast sandy expanse in northern Gaza.

Kitted up in full Israeli battle gear, young cadets sat in classrooms taking notes on lessons in combat tactics.

They showed off maneuvers where they simulated raining down mortars on mock-up tanks, on which two groups of fighters then pounced from nearby tunnels, with one combatant hoisting over his shoulder a limp volunteer posing as an Israeli soldier.

In addition to increasing the range and payload of more than 1,000 mostly homemade rockets it has hurled at Israel in two weeks, Hamas has stepped up its weapons procurement.

"Hamas leaders have tried to say through their statements that everything Israel's been hit with so far was completely and purely Gaza-made. (But) Hamas did not deny benefiting from foreign imports," said Gaza analyst Adnan Abu Amer.

Videos distributed by al-Qassam's media arm appear to show the strength of the group's arsenal.

"The demonstrated use of anti-tank guided missiles against small IDF units on foot, rather than against armored vehicles, shows a clear intent to simply inflict casualties and a recognition of the (Israeli army's) superior armor defense," said Charles Lister, a visiting fellow at the Brookings Center in Doha told Reuters.

In 22-days of fighting during a 2008-9 conflict, Hamas and other militant groups largely melted away, allowing Israeli tanks to approach the outskirts of Gaza City.

The fighters killed just six soldiers then, and two more in an eight-day round of battle in 2012, which did not escalate into an Israeli ground incursion.

Israel's loss of 12 soldiers on Sunday was the largest single-day toll since its forces pushed into South Lebanon in an attempt to dislodge Hezbollah fighters there in 2006.

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