More than 180 authors have signed an open letter to Eritrean president Isaias Afwerki demanding confirmation that 12 writers detained in 2001 are still alive.

Nobel prize-winning authors Olga Tokarczuk and JM Coetzee are among the high-profile signatories, alongside Colm Tóibín, Elif Shafak, Isabel Allende, Ben Okri, Yann Martel, Kamila Shamsie and Tsitsi Dangarembga. The letter was coordinated by PEN International and dated 18 September, marking 25 years since the government moved against Eritrea’s independent media. “Within days, Eritrea’s free press and the nation’s independent voices were systematically crushed,” the letter says.

It identifies 12 writers who have reportedly been held without contact with the outside world since 2001, among them poet Amanuel Asrat and playwright and journalist Dawit Isaak.

“The families of these writers, the Eritrean people and the global literary community have been met with a painful and unlawful silence,” the statement continues. “To withhold all information regarding their health, location, and survival is a violation of international law and an act of cruelty.”

Besides Asrat and Isaak, the letter names Dawit Habtemichael, Fessehaye “Joshua” Yohannes, Mattewos Habteab, Medhanie Haile, Sahle “Wedi-ltay” Tsegazeab, Said Abdelkadir, Said Idris “Abu Are”, Seyoum Tsehaye, Temesgen Ghebreyesus and Yousif Mohammed Ali. Six of those writers were the subject of profiles published in 2015.

Signed by 188 writers, the appeal calls for “immediate, verified proof of life for all arbitrarily detained Eritrean writers and critics”.

Additional supporters include Andrei Kurkov, Anthony Doerr, Chloe Aridjis, Lauren Groff, Lemn Sissay, Maaza Mengiste, Madeleine Thien, Margaret Busby, Max Porter, Philippe Sands, Preti Taneja, Tice Cin and Viv Groskop.

“Mr President, Eritrea’s future must be built with its brightest minds, not based on their suppression,” the letter states. “No writer or journalist should be disappeared for peacefully expressing their views.”

Eritrea has remained under Afwerki’s rule since gaining independence in 1993, and the country has not held national elections during that period.

“We remain in solidarity with our missing colleagues, and we will not cease our efforts until they are free,” the letter concludes.

Earlier this year, PEN International also began a public petition calling for verified evidence that the detained writers are alive.

“Twenty-five years is an unbearable length of time for any family to live without knowing whether a loved one is alive,” said PEN International president Burhan Sönmez. “These writers have not disappeared from our memory. We will continue to speak their names, and we will continue to demand the truth about what happened to them.”