GAZA, Aug 13 (Reuters) - A Fatah official said on Monday Hamas is holding 120 Fatah members in Gaza Strip jails, the first time the faction has given a detainee figure since the Islamist movement took control of the territory in June. Hamas has denied imprisoning Fatah men over their membership of President Mahmoud Abbas's faction, saying that only common criminals are behind bars. A Fatah official, speaking on condition he not be identified, said hundreds of Fatah members had been detained by Hamas's Executive Force since the brief civil war in Gaza two months ago. "Out of them, there are still 120 still in jail. Twelve others remain unaccounted for," the official said. Hamas spokesman Sami Abu Zuhri said the official's remarks were aimed at covering up what he said were the arrests in the West Bank of 420-490 Hamas supporters by the Fatah-dominated security services of President Mahmoud Abbas. "All the jails and centres are open to human rights institutions and the media in Gaza to check for themselves that we do not have a single political prisoner from Fatah or any other faction," Abu Zuhri said.