Nine IDF soldiers were killed Monday, the 14th day of Operation Protective Edge, including four killed by terrorists who infiltrated Israel from Gaza through a tunnel that emerged near Kibbutz Nir-Am.

The casualties brought the Israel Defense Forces death toll to 27 since the ground operation began last week.

The Israel Air Force killed 35 members of two Gaza families in separate strikes, near Khan Yunis on Sunday night and in Rafah Monday morning, according to witnesses. Also killed in the earlier air strike was Ahmed Sahmoud, 34, a known member of Hamas’ military wing, and the presumed target of that attack.

The four IDF soldiers killed near Nir-Am were: Lt. Col. Dolev Keidar, 38, of Modi’in; Sgt. Nadav Goldmacher, 23, of Be’er Sheva; Warrant Officer Baynesain Kasahun, 39, of Netivot; and 1st Lt. Yuval Heiman, 21, of Efrat.

With the death toll on both sides mounting, UN Secretary General Ban ki-Moon and U.S. Secretary of State John Kerry arrived in the region to try to help bring about a cease-fire. The two met in Cairo on Monday.

Netanyahu vowed Monday that the operation will expand until its goals are achieved. “The IDF is advancing on the ground according to plans, and the operation will continue to expand until its goal is achieved – restoring the calm to Israeli citizens for a long time,” he said after a meeting with Ya’alon, Chief of Staff Benny Gantz and the commander of the IDF Southern Command, Maj. Gen. Sami Turgeman.

The incident in which the four IDF soldiers were killed near Nir-Am occurred at about 6:30 Monday morning, when at least 10 Palestinians entered Israeli territory from the tunnel and split into two groups, one tried to make its way to Kibbutz Erez and the other to Kibbutz Nir-Am. The terrorists were wearing IDF uniforms, which confused the commanders in the field and led them to seek positive identification. Photos from airborne drones showed the “soldiers” were carrying Kalashnikov rifles, which are not used by the IDF, at which point the field commanders realized they were terrorists and opened fire. One of the cells, however, managed to fire an anti-tank missile at the military jeep carrying Keidar and his men, killing them on the spot.

During the firefight several of the terrorists tried to backtrack and make their way back to the Strip through the tunnel before the air force blew up the tunnel’s exit.

Nine bodies were later found, and the IDF believes that the rest of the terrorists succeeded in returning to Gaza.

The IDF believes the infiltrators were members of a Hamas force that was specially trained for this mission. In a video that documented the incident distributed by the IDF Spokesman one can see the terrorists were wearing regulation army boots, camouflaged helmets, and even had rubber bands tightening their trouser legs, making them look just like IDF soldiers.

Three Golani Brigade soldiers were killed in two different incidents early Monday morning in Gaza City’s Sujaiyeh neighborhood. In the first incident, Staff Sergeant Jordan Ben Simon, 22, of Ashkelon, was killed, apparently by misdirected IDF fire.

In the second incident, Staff Sgt. Tal Ifrach, 21, of Rishon Letzion, and Staff Sgt. Yuval Dagan, 22, of Kfar Sava, were killed in a firefight.

According to the IDF, since the ground operation began last week, 14 whole tunnels were exposed, and another 45 tunnel shafts were discovered, some of them in private homes and mosques. Hamas, the army said, has over the past decade considerably upgraded its tunneling capabilities; whereas in the past the tunnels were relatively short and 10 meters underground, the average tunnel depth today is 25 meters. Hundreds of thousands of man hours have been invested in tunnel construction, the army said.

Earlier Monday, the IDF released the names of six of the 13 soldiers who had been killed overnight Saturday and Sunday morning. They are: Master Sgt. Moshe Malko, 20, of Jerusalem; Maj. Tsafrir Bar-Or, 32, of Holon; Capt. Zvika Kaplan, 28, of Kibbutz Meirav; Sgt. Oz Mendelovich,21, of Atzmon, Sergeant Nissim Sean Carmeli, 21, a lone soldier from Texas who lived in Ra’anana; and Sgt. Gilad Yaakobi, 21, of Kiryat Ono.

The Gaza fatalities on Monday included 25 members of the Abu Jama’e family, who lived east of Khan Yunis, and 10 members of the Siyyam family in Rafah.

The home of the Abu Jama’e clan is a complex of eight apartments that houses the extended family. Fighter jets blew up the home on Sunday night while the family was eating its Iftar meal to break the Ramadan fast. Palestinian rescue workers labored throughout the night to rescue the wounded and retrieve the bodies.

From preliminary investigations by B’tselem and the Palestinian Center for Human rights, the attack was apparently not preceded by any warning, not even a “knock on the roof” missile. In addition to Sahmoud, the dead included a woman of 60, one of her sons, four of her daughters-in-law and 19 grandchildren aged four months to 14 years. Two of the women were pregnant.

In Rafah, the Siyyam home was bombed Monday, after morning prayers and the start of the fast. The strike also wounded 25 people.

According to the Palestinian Center for Human Rights, the IDF fired four warning missiles in the general vicinity of the Siyyam home; one landed in their garden, one hit a neighboring family, the Zuarovs, and the third and fourth hit the house of Ahmed Abu Sanima and wounded him. None of the three families knew which of the families the missiles were meant to warn.

The Siyyam family, however, began to evacuate its home on the assumption the warning was meant for them. The moment they left the house, a fifth missile landed right on them. Two men, their wives, and six children aged 9 months to 15 years were killed.

According to the Gaza Health Ministry, the number of Palestinian fatalities during Protective Edge is 508, among them 69 women and 130 children.