A Palestinian engineer is due in court on Thursday after he was allegedly detained in Ukraine and taken to Israel by force.
Dirar Abu Sisi, a director of a Gaza power plant, is accused of anti-Israeli activity, his lawyer in Tel Aviv says.
He says he was forcibly removed from a train in Kharkiv, eastern Ukraine, by Israeli agents last month, interrogated and flown out of the country.
The family of Mr Abu Sisi, 43, has held demonstrations calling for his release.
His friends and relatives reject Israeli reports that the engineer is affiliated to militant groups in the Gaza Strip and are calling on the Ukraine authorities to intervene.
Mr Abu Sisi's health is said to have deteriorated since he was taken to prison.
Israeli lawyer Smadar Ben-Natan says she has made urgent appeals to the United Nations Office of the High Commissioner for Human Rights, asking it to investigate.
Mr Abu Sisi left for Kiev on 19 February, intending to visit his brother and the family of his Ukrainian wife, reports say.
He told a legal group he was picked up by Israeli agents, handcuffed, hooded and then held in an apartment before being brought to Israel. He said he went 25 days before seeing a lawyer.
Israeli media were only able to confirm that the Palestinian man was being held a week ago, when a gag order was partially lifted.
This had been put in place at the request of the Shin Bet security service and the State Prosecutor's Office.