Isolating Hamas is counterproductive, Carter said. Hamas rules the Gaza Strip but is ostracized by Israel, the U.S. and European Union as a terrorist group.

"I think it is absolutely crucial that in the final and dreamed-about and prayed-for peace agreement for this region that Hamas be involved and Syria will be involved," he told a business conference outside Tel Aviv.

"I can't say that they will be amenable to any suggestions, but at least after I meet with them I can go back and relay what they say, as just a communicator, to the leaders of the United States," he said.