Extremists allied with Islamic State are believed to have executed Filipinos in a besieged southern city of the Philippines because they could not recite Islamic prayers, as the death toll from six days of fighting rose to 100, with dozens wounded.

The bodies of eight men, most of them shot in the head with their hands tied behind their backs, have been found on the outskirts of Marawi, 830 kilometres south of Manila.

Blood stains the roadside as civilians view bodies dumped in a ditch by militants. The eight executed men, who were hogtied, had a cardboard sign tied to their bodies bearing the word "munafik", or hypocrite. Credit:Getty Images

Residents who had fled the city told journalists the militants separated Christians and Muslims by those who could recite the prayers and took away those who could not.

Attached to one of the bodies was a sign that said "Munafik" (hypocrite).