More than 100 African writers and activists are urging Eritrea's authoritarian leader to protect basic freedoms and launch political reforms in the continent's "most closed society."

The open letter to President Isaias Afwerki expresses particular concern over the imprisonment of activists and journalists, including some allegedly denied regular visitation. It says a delegation of signatories should be allowed to visit.

Nobel laureate Wole Soyinka of Nigeria and pro-democracy campaigners such as Kenya's Boniface Mwangi are among those signing the letter.

It was not immediately possible to get Eritrean comment.

Eritrea last year made peace with neighboring Ethiopia after two decades of hostility, raising hopes that Isaias would relax his grip on the country he has ruled for 26 years.

Eritrea is the origin of many migrants trying to reach Europe.