Israel's ambassador to the United States, Michael Oren, says Israel has wanted to see Syrian President Bashar Assad removed from power since before the outbreak of war there - a shift from its publicly-stated position.

It sees his defeat by rebels who include Al Qaida-linked Islamists as preferable to his current alliance with Iran, Oren said.

His comments in an interview with the Jerusalem Post marked a move in Israel's public position on the civil war in Syria. Though old enemies, a stable stand-off has endured between the two countries during Assad's rule.

Unlike President Shimon Peres, Prime Minister Benjamin Netanyahu has stopped short of publicly urging Assad's overthrow and Israeli officials have long warned of the danger that al Qaida-aligned rebel forces could turn their guns on Israel if the Syrian leader fell.

But, Oren said: "The initial message about the Syrian issue was that we always wanted Bashar Assad to go, we always preferred the bad guys who weren't backed by Iran to the bad guys who were backed by Iran."

This was Israel's position well before the outbreak of war in Syria and had continued to be so, he added.

Assad's overthrow would also weaken the alliance between Israel's arc foe Iran and Tehran-backed Lebanese Hezbollah guerrillas, Oren said.

"The greatest danger to Israel is by the strategic arc that extends from Tehran, to Damascus to Beirut. And we saw the Assad regime as the keystone in that arc.

Oren described Al Qaida-aligned rebels as "pretty bad guys" but said that others were less radical.

Israel believes around one in 10 Syrian rebels are Sunni militants sworn to its destruction. Assad's Alawite sect is closer to the rival Shi'ite Islam of Iran and Hezbollah.

In the interview, excerpted ahead of its publication in full on Friday, Oren - a Netanyahu confidant - did not say if or how Israel was promoting Assad's fall.

Netanyahu casts Iran's disputed nuclear drive as the main threat to Israel and world stability.

Israel, which is widely assumed to have the region's sole atomic arsenal, has played down any direct Syrian threat to it but is concerned that a weak Western policy towards Assad could encourage Iran.