Child rights agency UNICEF has condemned the sentencing of a 13-year-old boy to 10 years in prison for blasphemy in northern Nigeria.

Omar Farouq was convicted in a Sharia court in Kano State in northwest Nigeria after he was accused of using foul language toward Allah in an argument with a friend.

He was sentenced on August 10 by the same court that recently sentenced a studio assistant Yahaya Sharif-Aminu to death for blaspheming Prophet Mohammed, according to lawyers.

Farouq's punishment is in violation of the African Charter of the Rights and Welfare of a Child and the Nigerian constitution, said his counsel Kola Alapinni, who told CNN they filed an appeal on his behalf on September 7.

Farouq was tried as an adult because he has attained puberty and has full responsibility under Islamic law.

Alapinni told CNN he or other lawyers working on the case have not been granted access to Farouq by authorities in Kano State.

He said he found out about Farouq's case by chance when working on the case of Sharif-Aminu, who was sentenced to death for blasphemy at the Kano Upper Sharia Court.

"We found out they were convicted on the same day, by the same judge, in the same court, for blasphemy and we found out no one was talking about Omar, so we had to move quickly to file an appeal for him," he said.

"Blasphemy is not recognized by Nigerian law. It is inconsistent with the constitution of Nigeria." the lawyer added.

He said Farouq's mother had fled to a neighboring town after mobs descended on their home following his arrest.

"Everyone here is scared to speak and living under fear of reprisal attacks," he said.

UNICEF, on Wednesday issued a statement "expressing deep concern" about the sentencing.

"The sentencing of this child -- 13-year-old Omar Farouq -- to 10 years in prison with menial labour is wrong," said Peter Hawkins, UNICEF representative in Nigeria.

"It also negates all core underlying principles of child rights and child justice that Nigeria -- and by implication, Kano State -- has signed on to."

Kano State, like most predominantly Muslim states in Nigeria, practices Sharia law alongside secular law.

CNN contacted a spokesman for the Kano State governor for comment but had not heard back before publication.

UNICEF has called on the Nigerian government and the Kano State government to urgently review the case and reverse the sentence, the organization said in a statement.

"This case further underlines the urgent need to accelerate the enactment of the Kano State Child Protection Bill so as to ensure that all children under 18, including Omar Farouq are protected -- and that all children in Kano are treated in accordance with child rights standards" Hawkins said.