Israeli Foreign Minister Avigdor Lieberman rounded on rightwing coalition partners Sunday, saying that snipes at US Secretary of State John Kerry's peace efforts risked estranging "a true friend."
"The man has a record of 29 years in the Senate. You can see all of his votes, all of his speeches," Lieberman told Israeli army radio.
"It's natural to have differences of opinion, but to call somebody anti-Semitic or an enemy of the people, or not an honest-broker because of differences of opinion? We shouldn't take friends and turn them into enemies," he said.
Kerry, trying to hammer out a framework agreement to advance Israel-Palestinian peace talks, came under fire from Israeli ministers after warning last week that the Jewish state faced growing delegitimisation if negotiations collapsed, also referring to "talk of boycotts".
Hardliners in the government of Prime Minister Benjamin Netanyahu were quick to lash out at Kerry.
One described his remarks as "offensive" and another accused him of working "to amplify" the boycott threat, prompting a terse statement from Washington urging Kerry's critics to get their facts straight.
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"It is sad to see that the US administration does not understand the reality of the Middle East and exerts pressure on the wrong side in the Israeli-Palestinian conflict," said Gilad Erdan, the minister for Home Front Defence and a close associate of Netanyahu.
Housing Minister Uri Ariel of the far-right Jewish Home party, which opposes a two-state solution to the conflict, told army radio that in raising the threat of a boycott, Kerry was not being "an honest-broker" in the negotiations.
Lieberman, a harsh critic of the Palestinian leadership and campaigner for Israeli Arabs to take an oath of allegiance or be stripped of their citizenship, has in the past been a less than welcome visitor in Washington.
But on Friday he sprang to Kerry's defence.
"We don't agree with Kerry over everything, but he is a true friend of Israel," Lieberman said at an economic forum."
His comment won praise from State Department spokesperson Jen Psaki.
"We certainly welcomed his remarks and his sentiment and the importance of the peace process," she briefed reporters on Friday.
"It certainly is a powerful statement and a powerful message given his history and his background on these issues and where his view was."