The IAF has been bombing the Gaza Strip incessantly since Wednesday evening in retaliation for intense rocket fire from the strip, with dozens of fighter jets striking more than 150 Hamas targets.
Early Thursday evening, the IDF destroyed a multi-story building at the Rimal neighborhood of Gaza City. The explosion shook buildings as dust and gray smoke filled the air, a Reuters witness said.
At least 18 people were hurt in the air strike, health officials said.
The five-story building, which is officially defined as a cultural center, was used by Hamas's interior security unit, which is responsible for all security operations carried out inside Gaza and is considered to be an executive branch of Hamas's political leadership.
The building served as the office of active unit members. A significant part of the unit's members are also Hamas military operatives.
Witnesses said the air force fired several warning missile at the building before the actual strike—a tactic that Israel uses to get people to evacuate buildings that are about to be targeted.
Hamas said that "Israel's targeting cultural centers, such as the Said al-Mishal Cultural Center, is a wild action that belongs to eras in which culture was fought against with fire and gunpowder."
"The attack on the al-Mishal center, which includes the offices of the Egyptian community in Gaza, is a Zionist attempt to destroy all of Egypt's efforts in the Gaza Strip. This is proof that Israel is the enemy of all elements of the Arab nation," Hamas added.
A source inside the strip also rejected claims Hamas used the building for its internal security forces, telling Ynet Hamas's internal security forces are housed in a nearby structure.
Before noon on Thursday, the IAF fighter jets attacked several terror targets up and down the Gaza Strip, including a military complex belonging to the East Rafah Battalion, an attack tunnel shaft east of Jabalia, and two Hamas attack tunnels near a beach in the central Gaza Strip.
The attacks, the army said, were "part of an ongoing effort to destroy underground terror infrastructure, which the IDF has been leading in recent years."
Over 20 sites attacked overnight
Overnight Wednesday, IAF jets targeted over 20 terror sites in military compounds and a Hamas training camp. Among the sites targeted were a weapons manufacturing and a storage facility, a complex used for the Hamas' naval force, and a military compound used for rocket launching experiments.
Additionally, five training camps were targeted as well as a main warehouse and a meeting point used by the senior commanders of the Khan Yunis Brigade.
The IDF Spokesperson's Office has also released exclusive footage showing an IAF aircraft striking a terror cell that launched several rockets into Israel only a few minutes earlier.
Palestinian officials said at least three people were killed in the Israeli attacks: Hamas fighter Ali Ghandour, 23-year-old Enas Khamash, who was pregnant, and her 18-month-old daughter Bayan. At least five civilians were wounded. Gaza's Health Ministry said the militant and the civilians were killed in separate incidents.
Kamal Khamash, brother-in-law of the killed woman, said the family was asleep when the projectile hit the house. The mother and daughter died immediately and the father is in critical condition, Kamal said.
"This is a blatant crime and Israel is responsible for it," he said.
"The timing of the escalation in Gaza and hurting members of the resistance while the Hamas delegation is in Cairo prove the Israeli enemy wants to sabotage the Egyptian and UN effort to calm the situation in the Gaza Strip," Hamas spokesman Fauzi Barhum charged.
He said Israel was responsible for everything happening in the strip, "and the resistance's response is natural—a response to the Israeli crimes an effort to force it to honor the ceasefire understandings from before."
Barhum called on decision makers in the region and the world "to intervene in order to stop this escalation and the harm to the residents and the members of the resistance."
Hamas spokesman Sami Abu Zuhri also blamed Israel for the escalation, citing the killing of two Hamas gunmen on Tuesday in northern Gaza which he described as unprovoked.
Israeli media reports said fire from the gunmen had apparently been part of a Hamas exercise and not directed at Israel. However an Israeli military spokesman said Hamas operatives had shot in the general direction of Israel's border.
The incident occurred while a group of senior Hamas leaders from abroad were visiting Gaza to discuss the ceases-fire efforts with local leaders.
A top Hamas official told The Associated Press that the group waited for the delegation to leave Gaza before responding with rocket fire late Wednesday.
Elior Levy, Yoav Zitun, Ilana Curiel, Matan Tzuri, Itamar Eichner, The Associated Press and Reuters contributed to this report.