JERUSALEM -- Israel's military said Sunday it stuck 18 Hamas targets in Gaza, responding to an explosive device that wounded four soldiers along the fence between Israel and the Palestinian enclave.

Palestinian medical sources said that at least two Palestinian youths were killed in the strikes, according to the official Palestinian news agency of WAFA.

An Israeli military spokesperson said in a statement that the strikes, carried out on Saturday night and early on Sunday morning, were made in retaliation to an explosive that denotated near the fence when a military patrol arrived to remove a "suspicious flag."

Four soldiers were injured.

Shortly later, the Israeli air force launched a large-scale attack. The assault included airstrikes of a tunnel built by Hamas, the Palestinian Islamist group that runs Gaza, in the Zaytun neighborhood in Gaza city; a military compound near Deir el Balah in the central Gaza Strip; and a military compound in the area of Khan Yunis in the southern Strip. Additionally, a tank targeted two observation posts, the military said.

"The IDF (Israel Defense Forces) views with great severity the incident," the spokesperson said.

"The Hamas terror organization is accountable for this incident and its consequences, as well as everything happening in and from the Gaza Strip, above and below ground," the spokesperson added.

The incident came amidst a looming humanitarian crisis in the Gaza Strip, a territory that has been under an Israeli and Egyptian blockade since 2007.

Israel seized the Gaza Strip, along with the West Bank, in the 1967 Middle East war and has kept its control over the territory despite international criticism.