A senior Hamas official says prisoner swap talks with Israel have hit a snag over some of the top militants the Islamic group wants freed.

The official, who spoke on the condition of anonymity because of the issue's sensitivity, says a deal is unlikely in coming days to release Israeli soldier Sgt. Gilad Schalit, seized by Gaza militants in 2006.

He said Wednesday the German mediator shuttling between the sides has presented an alternative list of names provided by Israel, and that Hamas leaders are studying it.

Officials on both sides have warned that a deal may not be eminent even though Israeli and Hamas negotiators have expressed cautious optimism in recent days over the progress of negotiations.