The government of Slovenia says a special presidential envoy to Sudan is to be tried on charges of espionage and entering Sudan illegally.
Some two million people have fled the fighting in Darfur
The envoy, Tomo Kriznar, was involved in the peace process between the Sudanese government and the rebels in the troubled region of Darfur.
He was arrested last month for not possessing a valid entry visa.
At a court hearing he denied the spying charges but admitted entering Darfur without a Sudanese visa.
According to the Sudanese official news agency Suna, court proceedings against Mr Kriznar started on Monday in Al-Fashir, Darfur's largest town.
Mr Kriznar told the court that he had applied for a visa at the Sudanese embassy in Vienna but had been refused, Suna reported.
Tomo Kriznar, 51, is well known in Slovenia as a human rights activist.
He travelled to Darfur in February as the Slovenian president's envoy.
Three months ago, Slovenia held talks with two rebel movements which refused to accept a peace agreement between the main rebel faction and Khartoum.
Sudanese investigators said Mr Kriznar was travelling around Darfur taking pictures and shooting video material of villages there, Suna reports.
The conflict in Darfur, a vast region in western Sudan, started in 2003 when members of ethnic African tribes rebelled against the Arab-led government in Khartoum.
Sudan's government is accused of sending militias to attack Darfur civilians.
It is estimated that more than 200,000 people have died and more than two million have fled their homes in the conflict.
A peace plan agreed to in May is still being opposed by some rebel groups.