Malcolm Hoenlein, executive vice chairman of the Conference of Presidents of Major American Jewish Organizations, said the alliance is "very disturbing" to many American Jews. He said there are also concerns that it will provide new ammunition for Israel's critics.

Netanyahu last week welcomed a merger that folded the "Jewish Power" party into the larger "Jewish Home" for April elections. As part of their deal, Netanyahu gave the merged party a seat on his Likud Party's list of candidates and guaranteed them two Cabinet positions if he wins.

"Jewish Power" members see themselves as the ideological heirs of the banned Kach movement, which was outlawed by Israel and the US because of its racist views.

The deal has been widely criticized in Israel, and even strong supporters of Israel in the US have spoken out against it. The American Jewish Committee, a major pro-Israel advocacy group, and the pro-Israel lobbying group AIPAC both called Jewish Power "reprehensible."

"For those who follow this, there's a lot of concern," Hoenlein said in an interview.

"What we have to deal with is how it is perceived and understood in the United States," Hoenlein said. "And we have to be very careful because it feeds certain tendencies that are very concerning to us."

Hoenlein, who is visiting Israel, said he has not discussed the matter with Netanyahu and did not want to judge him. "He obviously has some political calculation that drove him to it, but politics can't dictate everything. You have to take into consideration all of the ramifications and all of the concerns," Hoenlein said.

Hoenlein said, however, that the "ultimate decision" will be made by the Israeli public, which he said rejects extremism.

Netanyahu on Saturday lashed out at his domestic critics on Saturday, claiming they have sought alliances with extremist Arab parties and accusing them of hypocrisy.