(CNN) -- Afghan authorities will investigate the sudden illness of students and staff at three schools in the past week in northern Afghanistan, the Afghan Human Independent Rights Commission said on Sunday. Local doctors suggested the Taliban may be the perpetrators of possible poison attacks.

"During the last seven days three cases of poisoning [have] occurred in Kunduz Province," said Syed Karim Talash, the director of the commission office in the province.

At least 88 girls and teachers became ill in separate cases at three girls' schools.

The cause of the illnesses was not known, but Talash said poison gas was suspected.

"It is really big concern for us, and big concern for the family of the girls," Talash said.

Dr. Mohammad Qasam Khamoosh, who treated girls from two schools, said "unknown gases" were responsible for the mass illnesses.

These are "terrorist activities against education in the country," he said.

Girls were not allowed to attend school during the Taliban's rule. Girls' schools have been open in the region since 2001.

Khamoosh said authorities were able to gather a sample of the gas, which has been sent off for testing.

Kunduz province has seen a drastic influx in terrorist activity, particularly by the group known as Hizb-e-Islami, led by the notorious leader Gulbudeen Hekmatyar. It's an independent group that has increasingly worked under the Taliban umbrella in recent years.

CNN's Atia Abawi and journalist Muhib Habibi contributed to this report.