At least 50 Palestinian Arabs were wounded in a blast that occurred Thursday inside a training camp for terrorists in Gaza, Hamas officials, medics and witnesses said, according to AFP.

“An explosion happened inside a post of the resistance in Beit Lahya,” said interior ministry spokesman Iyad al-Bozum, in reference to the Izz ad-Din al-Qassam Brigades, Hamas’s so-called “military wing”.

The health ministry spokesman in Gaza, Ashraf al-Qudra, said the blast wounded 50 people, five of them in a serious condition, and including children.

Witnesses said the blast took place inside a training camp of the Izz ad-Din al-Qassam Brigades in northern Gaza, where Hamas is the de facto power.

A doctor in the enclave, Baker Abu Safia of Al-Awda Hospital, said 30 wounded people were brought to his establishment, most of them women and children.

He said the hospital “declared a state of emergency” after the explosion took place.

The cause of the explosion is not yet known nor is it known who is behind it, but it comes one week after  a Salafist group in Gaza that is affiliated with ISIS threatened to kill Hamas members “one by one” in retaliation for the arrests of its members.

Last Friday, those threats appeared to be edging to fruition, after an ISIS-affiliate in the Sinai Peninsula claimed it launched two “bombs” at Hamas posts in Gaza.

There have also been explosions in Gaza related to the failed Hamas-Fatah reconciliation pact, as the sides continue to quarrel despite forming a unity government last year.

In addition, there have been “work accidents” in the region, involving terrorists who are in the midst of preparing an explosive device.