The lawyer for a Gazan engineer held under secrecy in Israel accused authorities on Wednesday of concocting charges against him after seizing the Palestinian overseas.

Relatives of Dirar Abu Sisi, a manager of the Gaza Strip's main power plant, say he was abducted from a train in Ukraine last month. Israeli officials have confirmed he is in custody but declined further comment, citing court-issued gag orders.

Smadar Ben-Natan, Abu Sisi's attorney, linked his detention to Israel's efforts to gather intelligence on the hostile, Hamas-ruled territory, frequent site of cross-border fighting and the 4-1/2-year captivity of an Israeli soldier.

The Mossad spy agency and other Israeli security services have in recent years ramped up efforts to disrupt weaponry and cash smuggling to Hamas from foreign sponsors such as Iran.

"When someone came along who they thought was senior (in Hamas) and was located outside the Gaza Strip, they got their hands on him, without this matter being really justified, in retrospect," Ben-Natan said on Israel's Army Radio.

German newspaper Der Spiegel on Tuesday quoted an unnamed source as saying Israel may have suspected Abu Sisi of knowing the whereabouts of Gilad Shalit, the captive soldier.

But Ben-Natan said Abu Sisi denies having any connection to Shalit. No mention of the soldier was made in allegations lodged against Abu Sisi by Israeli prosecutors in closed-door remand hearings, she added.

According to sources in Gaza, Abu Sisi was not known to have political affiliations to Hamas.

Ben-Natan did not, in the radio interview, elaborate on the state's suspicions against Abu Sisi. But she said the court sessions had led her to believe "they are trying to cover up the mistake" of seizing him.

"Instead of confessing and saying, 'Sorry, turns out what we thought was a mistake, we are sorry, go home, Sir,' they are trying to find what they can blame him with so that it doesn't became clear this whole matter was one big farce," she said.

Israeli security and justice officials declined to respond.

Abu Sisi was scheduled to appear at another remand hearing on Thursday. Ben-Natan, an Israeli, said she expected to know then "how the state intends to indict (him), if at all".

The case has further potential to embarrass Israel should it emerge that Abu Sisi was spirited out of Ukraine without Kiev's approval. The Palestinian's wife, a native of Ukraine, said he had gone there in a bid by the family to immigrate from Gaza.

Visiting Israel this month, Ukrainian Prime Minister Mykola Azarov said Abu Sisi's disappearance was under investigation.

Asked in a newspaper interview about the possibility that the Palestinian had been abducted by Israeli agents, Azarov said: "I don't want to imagine that such things are carried out on the soil of a friendly state."