Israeli war jets carried out around 19 airstrikes on posts and positions belong to the Hamas movement in the Gaza Strip, medical and security sources said Monday.

Ashraf al-Qedra, Gaza Health Ministry spokesman, told reporters that at least three civilians were lightly to moderately injured in the airstrikes, which began in the morning. Israeli artillery also participated, sources said.

The airstrikes came after unknown militants fired a makeshift rocket from northern Gaza into southern Israel earlier in the morning, according to Israel Radio. No injuries were reported.

Mohamed al-Meidana, Gaza Civil Defence spokesman, told reporters that two of the strikes targeted two military training facilities that belong to the al-Qassam Brigades, the armed wing of Hamas in northern and central Gaza.

Hamas spokesman Abdulatif al-Qanou said in an emailed press statement that his movement holds Israel responsible for the current military escalation on the Gaza Strip and will be responsible for the consequences.

"The occupation is trying to export its internal corruption crisis to the Gaza Strip. Therefore, the role of the Palestinian resistance is to defend our people from this aggression," he said.

It was the first time since October that Israel had officially reported that a rocket fired from Gaza had reached Israel since October.

In 2014, Egypt brokered a ceasefire between Israel and Hamas ending a 50-day Israeli air and ground military offensive on the Gaza Strip, which left around 2,200 Palestinians and 70 Israelis dead.