Gavri Bargil, one of the leaders of Peace Now, an Israeli peace organisation, said: "I think the work Aipac does is crucial and I support them. Our fear is sometimes they are too successful.
"They do not always represent the line of the Israeli public, nor the Jewish community in the US, who believe in two peoples, two states.
"Many times what Aipac reports to the [Capitol} Hill or to the US administration is much out of line."
Steve Clemons, of the New American Foundation, a Washington think-tank, said: "I am impressed with the organisation and there's a lot of jealousy of its success.
"It has successfully managed to narrow debate in Washington on the Palestinian issue.
"We have a cartel of institutes and political think-tanks that dominate this area and I think it would be healthier if there were more players.
"... it would be a nice idea to invite Keith Ellison, the first Muslim member of congress into a conversation at the conference.
"That kind of activity would go a long way to demystifying Aipac and what it's about, because there is a bit of mystery about what it is, and isn't, about."
Morton Klein, a member of the executive committee of Aipac, said: "George Bush has refused to move the US embassy from Tel Aviv to Jerusalem, George Bush has relentlessly pressured Israel to accept the road map and make concessions to Palestinians.
"The only reason Aipac has success in Capitol Hill is not because of its lobbying efforts per se.
"It's because the vast majority of American citizens, who are primarily Christians, support Israel over the Palestinian Authority by between three-to-one and five-to-one, depending on which poll you use."
Source: Al Jazeera