A Christian man who was jailed for praying has died in Laos after he was denied vital medication.

Tiang Kwentianthong was imprisoned along with four others after praying for healing for an elderly woman, according to a human rights group. Tiang, who suffered from severe diabetes, died shortly after being released because his condition was ignored by officials.

"During his imprisonment in Savannakhet provincial prison, Mr Tiang requested permission to be treated for his worsening diabetic condition but the prison officials denied his request," a statement from the Human Rights Watcher for Lao Religious Freedom (HRWLRF) read.

The married father of six was arrested in June 2014 in Saisomboon village in the Savannakhet province of Laos. He was found guilty of conducting treatment without medical authorisation after praying for the healing of an elderly woman.

In deciding the case, the People's Court of Savannakhet province equated healing prayer with medical treatment, which requires medical authorization from the Ministry of Health. As a result Tiang and four other Christians were convicted of violating medical law.

The verdict did not have proper factual and legal basis according to HRWLRF. The group say he was arrested and imprisoned illegally.

"The HRWLRF demands that the Lao government with the Savannakhet provincial prison officials take responsibility for the death of Mr Tiang who was arrested and imprisoned illegally and who was denied request for medical treatment for his worsening diabetic condition," the statement read.

Tiang's fellow prisoners have appealed their case. However, although in Lao law the Court of Appeal must make a judgement on an appeal case with 45 days, the case is now 157 days beyond the time limit.