* Ghanaja's body hidden in cupboard, home set on fire
* Hamas says trying to find who responsible
* Ghanaja had planned to leave Syria, as many Hamas officials have done (Adds details of assassination)
GAZA, June 28 (Reuters) - Hamas said on Thursday that one of its members, Kamal Husni Ghanaja, had been killed in his home in Damascus and that it was trying to find who was behind what the Palestinian Islamist group described as a "cowardly murder".
Hamas, which rules the Gaza Strip, said in a statement that it was trying "to identify the party behind the deplorable crime", but did not immediately accuse Israel, its long-time enemy, of involvement in the killing.
A Palestinian source with ties to Hamas said Ghanaja's charred body was found in a cupboard above the ceiling of his ransacked apartment in the Qudsia neighbourhood of Damascus. A Hamas source said there were marks of torture on his body.
"The charred, scarred, body was concealed in a ceiling closet and a fire had engulfed the house which apparently the assassins had started," said the source. The body was found on Wednesday, but most indications suggested Ghanaja was killed a day earlier, the source said.
Hamas said Ghanaja, alias Nizar Abu Majahid, had "spent his life working for the sake of God" within its ranks, but did not disclose his exact role.
One Hamas source described Ghanaja as a mid-level military official. Another Palestinian official said he was in charge of the movement's organisational network in Syria.
Damascus has for years been a base for Hamas's leadership in exile but many of the group's top officials and their families have left during the past 16 months of violence in Syria.
One Palestinian official said Ghanaja had been planning in recent weeks to leave the Syrian capital and join his family who now live in neighbouring Jordan.
Asked about reports of Ghanaja's death, Israeli Defence Minister Ehud Barak told Israeli Army Radio: "He was not really personally familiar (to me). According to all the background published, he was no saint and I don't want to add anything or comment about this incident."
"It is definitely possible that not only Israel (was after him," Barak said.
Israel's Mossad intelligence service is widely believed to have been behind the assassination in Dubai in 2010 of Mahmoud al-Mabhouh, a top Hamas commander. Israel refused to confirm or deny its agents killed him.
Mabhouh's killers smothered him in his hotel room, apparently trying to make it look as if he had died of natural causes. (Reporting by Nidal al-Mughrabi in Gaza and Maayan Lubell in Jerusalem and Suleiman al-Khalidi in Amman, Writing by Jeffrey Heller in Jerusalem; Editing by Tim Pearce)