Red Cross officials in Afghanistan say they have provided medication for 40 prisoners on hunger strike at Kandahar men's prison.
The men are among around 300 inmates who have been refusing food for a week, demanding the chance of a fair trial.
They are also demanding that American forces stop what they say is the harassment of their families while they are locked away.
Correspondents say the protest is restricted to one block of the prison.
The men, some of them on remand, say they have been held for years due to long delays in the judicial process.
The authorities have rejected claims by prisoners that there has been official interference in individual cases.
Prisoners say they have been denied the right to appeal as well as legal advice.