Dirar Abu Sisi vanished from a sleeper train in Ukraine in February and mysteriously resurfaced days later in an Israeli prison, recalling the dramatic covert operations Israeli was once famous for.

His abduction comes during an escalation in tensions between Israel and Hamas that many fear may rekindle full-scale fighting.

The case of Abu Sisi has been veiled in secrecy since his family came forward last month saying he was snatched by Israeli operatives in Ukraine.

Israeli authorities placed a gag order on the case, until the release of Monday's indictment, though it still refuses to say how the 42-year-old Gazan was caught.

The indictment accused Abu Sisi of masterminding the militant group's rocket program and charged him with hundreds of counts of attempted murder, conspiracy to commit murder and production of weapons.

Abu Sisi denied all the charges and his Israeli lawyer, Smadar Ben-Natan, said the indictment was "inflated, exaggerated and unconnected to reality."

The indictment described alleged meetings and conversations he held with Hamas operatives as far back as 2002.

"Abu Sisi's ongoing and significant activities in Hamas' service over the past decade, with an emphasis on strengthening and improving the capabilities of Qassam rockets, allowed Hamas to create a growing threat to the Israeli home front, resulting in the death and wounding of many Israeli civilians," it said.

After the hearing, Ben-Natan accused Israel of torturing her client and forcing him to sign Hebrew documents he did not understand. "We are going to ask to dismiss this indictment because of the abusive process that has been done to this person and the illegality of his detention," she said.

During a brief courtroom appearance, Abu Sisi, a senior engineer at Gaza's sole power plant, professed his innocence and accused Israel of trumping up charges against him in a futile attempt to gather information about Gilad Schalit, an Israeli soldier captured by Gaza militants nearly five years ago.

"I don't have any connection with Schalit and the investigation proved that," he said. "When they found out I don't have any connection to Schalit, they fabricated these charges."

His family denied he belonged to Hamas or was a militant.

"He has been slandered," Abu Sisi's Ukrainian wife, Veronika, told The Associated Press in Ukraine. "My husband has never been involved in those horrors."

In Gaza, Hamas spokesman Sami Abu Zuhri denied the engineer is a member.

"He is a Palestinian citizen kidnapped in a criminal gang-style operation while he was visiting his family in Ukraine, and all the Israeli accusations are only to justify his abduction," he said.

Robbie Sabel, a former legal adviser to Israel's Foreign Ministry, said that under international law, it is irrelevant how Abu Sisi was brought to Israel. "Once somebody is in the country, he is within jurisdiction," he said.