Eight Christians who were killed when an Islamic State-linked group stormed a Filipino city late last month were shot to death because of their refusal to recite the Islamic declaration of faith, government officials have reportedly said.

According to the Christian persecution monitoring website Morning Star News, eight Christians who were among the 19 killed when the IS-aligned Maute Group stormed the city of Marawi on May 23 were the first Christians killed during the insurgent uprising in the capital of Lanao del Sur Province on the Mindanao island. The city, which was once home to over 200,000 residents, has seen thousands of residents flee in recent weeks.

The same extremist group claims it is responsible for the kidnapping of as many as 240 Catholics, including Father Teresito "Chito" Suganob, the priest who appeared in a recently released video in which he listed off the names of other "prisoners of war" who were captured by the militants.

Morning Star News reports that government investigators told local media that the eight Christians killed in the May 23 assault were laborers who were stopped by dozens of militants while fleeing to the city of Iligan.

The investigators explained that the militants tied their hands and asked them to recite the Shahada. When they refused, the militants shot them. The investigators added that the militants then placed the bodies into a ditch and put a sign next to them that read "Munafik," which means traitor or liar.

The eight Christians were not the only ones shot and killed for refusing to recite the Islamic creed. Police inspector Freddie Solar, whose religion was not identified, also refused and was shot by the militants, according to his wife.

NPR reported on Thursday that as many as 19 civilians, 39 soldiers and 120 militants have been killed since the government lost control of the city last month.

According to Catholic News Agency, the militant group formed in 2012 and officially pledged its allegiance to the Islamic State in 2015. But the group's violence drastically increased after a failed attempt from the Filipino military to arrest a local extremist leader by the name of Isnilon Hapilon.

Since the assault began in Marawi in May, the Maute Group has burned down a number of buildings, which include a Catholic cathedral and bishop's residence.

The Associated Press reports that military spokesman Restituto Padilla said on Tuesday that about 1,000 residents remain trapped in the city and over 900 have been rescued by government forces. Additionally, the military has killed a total of 89 militants and has liberated about 90 percent of the besieged city.

Padilla added that the extremists group's video featuring Father Suganob appears to be authentic but warned that is being used for propaganda.

In the video, Suganob, the vicar general of the prelature of Marawi, calls on President Rodrigo Duterte for help and tells him that the militants "don't ask for anything ... they just ask that you leave this place peacefully."

This article was originally published in The Christian Post.