Thirteen soldiers were killed overnight when they encountered fierce Hamas fighting in the dense urban environment of Gaza City, the IDF announced Sunday evening.

The central battle began when an anti-tank mine exploded under an Israeli armored personnel carrier, killing seven soldiers from the 13th battalion of the Golani Brigade, the army said.

The ambush, supported by machine gun fire, took place in the Shejaiya neighborhood of Gaza City, in the northern part of the 40-kilometer-long Strip. The other soldiers were killed in the same neighborhood, a Hamas stronghold that is home to some 100,000 people.

In the overnight fighting, an unspecified number of soldiers were also wounded, including Col. Ghassan Elian, the commander of the Golani Brigade, whose wound was deemed light to moderate.

An Israeli soldier, wounded in Gaza, is evacuated near the border on July 20, 2014. (Photo credit: Flash90)

An Israeli soldier, wounded in Gaza, is evacuated near the border on July 20, 2014. (Photo credit: Flash90)

The army later published the names of five of the fallen soldiers late Sunday night: Maj. Tsafrir Baror, 32, of Holon; Capt. Tsvi Kaplan, 28, of Kedumim; Sgt. Gilad Rozenthal Yacoby, 21, of Kiryat Ono; Sgt. Oz Mandelovich, 21, of Avtalion; and Nissim Sean Carmeli, 21, of Ra’anana.

The families were informed earlier on Sunday. All the 13 fatalities were from the Golani Brigade, the army said.

The IDF on Sunday dismissed rumors that one or more soldiers had been abducted.

The army said it had killed 130 Hamas fighters since the start of Operation Protective Edge. Military sources said the fighting in Shejaiya would likely continue for several more days.

The IDF also said it had found a 15th Hamas tunnel dug under the Israeli border, near Moshav Netiv HaAsara, through which it said Hamas had planned a terror attack on Israeli civilians.

The incident in which seven soldiers were killed took place shortly after 1 a.m. Sunday, IDF sources said. Two more soldiers were killed in exchanges of gunfire with Hamas 20 and 30 minutes later. Three more soldiers were killed when an anti-tank missile was fired into a building in which they were setting up a command post. The 13th fatality was still being investigated by the IDF late Sunday, but was believed to involve fatal fire by IDF troops in a case of mistaken identity.

IDF Chief of General Staff Benny Gantz said the IDF would not be deterred by the deaths from its mission, to restore sustained security from Hamas attack for Israel’s citizens. He said the IDF would “learn from the incident” and that “the enemy had prepared” for conflict with Israel.

“In battle there are casualties, but our role is to fulfill missions –- and we will continue in that,” said Lt. Gen. Gantz. “The residents of Shajaiya, too, know that they fell victim to the deployment of Hamas personnel in the neighborhood.”

To the “misfortune of Gaza’s residents,” Gantz said, Hamas “instead of building houses, schools, hospitals and factories” had built a war machine in residential areas.

He said Israel mourned the loss of life and injury among Gaza civilians, but emphasized that Israel had repeatedly warned residents of the area to evacuate because Hamas had deployed there. “We issued warning after warning,” he said, making phone calls, distributing leaflets and more. He said the IDF would make “every effort” to prevent civilian casualties, and that Israel was sending aid into Gaza, and had opened a field hospital on the border. No other army or country would act in this way, he said. But “in the end there is a mission, a moral obligation” to protect the people of Israel.

Overall, said Gantz, the IDF offensive against Hamas was proceeding well, and the soldiers were doing “fantastic work.” He said: “I’m proud of them. All of Israel should be proud of them.”

Hamas was losing “more of its people, more capabilities, more infrastructure” hour after hour. “We will maximize our achievements” Gantz said, and “strip them of their capabilities.” He urged the Isreli public to be patient and stand firm.

The ambush in which the seven soldiers were killed triggered a heavy aerial bombardment of the area, prompting thousands of residents to flee on foot, AFP reported. Reports quoted Palestinian medical officials in Gaza saying that more than 70 Palestinians, among them many civilians, were killed in the fighting. Thousands more fled the neighborhood.

Israeli officials said Shejaiya is a Hamas stronghold, and that 150 rockets had been launched from that area in the past two weeks. Israeli military officials said Sunday that they had told civilians to leave the Shejaiya area days ago, ahead of IDF military action. Hamas has repeatedly told Gazans not to heed the Israeli warnings.

An army spokesperson added that the IDF has not been surprised by Hamas fighters’ willingness to engage its forces, saying it was “in line with our planning and assessments.”

The army, which has increased its troop presence in the Gaza Strip, reports having killed 130 gunmen since the ground operation began on Thursday night.

Much of the conflict over the past day has taken place in the north of the Gaza Strip.

The army found and demolished two tunnels in the area, stretching toward Kibbutz Zikim and Kibbutz Netiv Ha’asara, and an additional 14 tunnels were being explored and readied for demolition.

IDF spokesman Lt. Col. Peter Lerner said that much of the fighting has taken place in and around the tunnels. “Hamas are really trying to defend their tunnel infrastructure,” he said.

Lerner added that beyond the east-west tunnels dug in order to carry out attacks within Israel, the army has seen an array of offensive tunnels used within Gaza, in order to facilitate rocket fire and ambushes on incoming troops. “There’s a whole underground Gaza,” he said.

Four other IDF soldiers were killed in fighting earlier Saturday.