The Muslim American Society will investigate an event at a Philadelphia Islamic Center last month at which children sang violent songs which the organization says were not "properly vetted."

The group called the incident "an unintended mistake and an oversight," the Philadelphia Inquirer reports.

A video of the event published by the Middle East Media Research Institute (MEMRI) shows children singing violent lyrics. One girl says "we will chop off their heads" to "liberate the sorrowful and exalted Al-Aqsa Mosque" in Jerusalem.

"We will defend the land of divine guidance with our bodies, and we will sacrifice our souls without hesitation. We will lead the army of Allah fulfilling his promise, and we will subject them to eternal torture," a girl reads.

Children also sang about the "blood of martyrs" and "Rebels, rebels, rebels."