In another worrying sign that US President Donald Trump might not be as wholly on Israel's side as some might have hoped, the Trump State Department on Thursday rebuffed its own ambassador to Israel for legitimizing Jewish settlements.

Marking the 50th anniversary of Israel's resettlement of the biblical heartland of Judea and Samaria, US Ambassador David Friedman told the Walla news portal that the "settlements are part of Israel."

Friedman explained that the various UN resolutions upon which the peace process is based never required Israel to surrender the entirety of the territory it liberated from Jordanian occupation in 1967.

The Trump State Department's reaction was both swift and harsh.

"I just want to be clear that our policy has not changed," said State Department spokesperson Heather Nauert, stressing that Friedman's remarks represent his views along, and should "not be read as a shift in US policy."