Rival US power brokers Haim Saban and Sheldon Adelson issue warnings to their parties

The billionaire political kingmakers planning to bankroll much of the 2016 presidential campaign have put aside their differences to speak out together with blunt warnings on key issues for their respective parties.

Haim Saban, a media mogul and close Democratic ally of Hillary Rodham Clinton, criticised President Barack Obama's outreach to Iran, declaring that "we've shown too many carrots and a very small stick".

Sheldon Adelson, a casino magnate who is likely to tap into his fortune in an effort to elect a Republican to the White House, upbraided many in the party for their opposition to legalising millions of undocumented immigrants. Without a comprehensive overhaul, he said, the country would not be "the America that I'm proud to live in".

Adelson, 81, and Saban, 70, have gained enormous power in the new era of super political action committees and unlimited contributions. Both made it clear during a rare joint appearance on Sunday, before an audience of several hundred Israeli-Americans, that they intended to assert that power during the next presidential campaign and beyond with policy demands for their candidates. In particular, they vowed to press both sides for a more hawkish approach to the Middle East.

Appearing before a group called the Israeli American Council, both men called for unity when it comes to support for the Jewish state, reminding all prospective presidential candidates of the primacy of the US-Israel relationship. And they agreed that Obama and his administration have not been tough enough in protecting Israel's interests.

In an interview with The Washington Post, Saban described the president's relationship with Israeli Prime Minister Benjamin Netanyahu as "like oil and water". That had fed a perception, he said, that Obama has not been a friend to Israel. But Saban thought that, in reality, "there's never been this level of cooperation with any previous president".