A former official at the UN war crimes tribunal at The Hague is being kept in isolation with lights permanently on, her lawyer says.
French journalist Florence Hartmann, once a court spokeswoman, was arrested over a 2009 conviction for contempt for disclosing confidential documents.
She was initially sentenced to a fine, but this changed to seven days' jail when the court ruled she had not paid.
Hartmann, 53, had insisted the money was deposited in a French account.
She was arrested on Thursday in The Hague, where she had gone for the verdict against former Bosnian Serb leader Radovan Karadzic.
Her lawyer, Guenael Mettraux, told AFP news agency she was being kept "under suicide watch conditions, meaning with light in her cell 24-hours a day and that she is being checked on every 15 minutes by the guards" in a detention unit at the Hague tribunal.
"She is isolated from other detainees and so far has only been visited by the French consul," he said.
He had filed applications for the conditions of detention to be changed and for her early release. But he said there was literally no-one available to deal with them until after the Easter break.
Mettraux told UK daily the Guardian that his client had said she was in the bizarre position of "watching Gen Ratko Mladic [the Bosnian Serb military leader accused of war crimes] walking around the yard and associating with other prisoners while I'm locked away in a cage".
Hartmann worked for the International Criminal Tribunal for the Former Yugoslavia from 2000 to 2006.
She wrote a book, Peace And Punishment, and an article in which she disclosed the existence of confidential documents on the Serbian government involvement in the Bosnian war of the 1990s.