JERUSALEM, March 20 (Reuters) - Israel acknowledged on Sunday it was holding and investigating a Gaza engineer but banned details of the Palestinian's arrest, which his relatives said was carried out as an abduction last month in Ukraine.

Relatives of Dirar Abu Sisi, a manager of the Gaza Strip's main power plant, say he was abducted from a train in Ukraine.

A spokeswoman from Israel's courts told Reuters that Abu Sisi was being held in Israel and is being investigated, but gave no other details.

Israeli officials until now have declined all comment, citing a court-issued silencing order.

An official for an Israeli human rights group said Abu Sisi was being held at a prison in southern Israel and has been in Israeli custody since Feb. 19.

Abu Sisi is one of the managers of the main power plant in Hamas-ruled Gaza, but was not otherwise known to have any political affiliation with the Islamist group.

(Writing by Ari Rabinovitch)