The United States has objected to the appointment of a former Palestinian prime minister to lead the UN political mission in Libya, saying it was doing so to support its ally Israel.

Nikki Haley, US ambassador to the UN, said on Friday that her government "was disappointed" to learn that Antonio Guterres, UN secretary-general, planned to appoint Salam Fayyad as the special representative.

Fayyad served as the Palestinian Authority's prime minister from 2007-2013.

Appointments of the UN special representatives of the secretary-general require the unanimous backing of the 15-member council.

It was unclear whether the objection had ended Fayyad's candidacy.

The US wields significant influence as one of the five permanent members of the UN Security Council.

"For too long, the UN has been unfairly biased in favour of the Palestinian Authority to the detriment of our allies in Israel," Haley said. "Going forward, the United States will act, not just talk, in support of our allies."

Guterres later on Saturday defended his choice, saying it "was solely based on Mr Fayyad's recognised personal qualities and his competence for that position".

"United Nations staff serve strictly in their personal capacity. They do not represent any government or country," he said.

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Al Jazeera's Rosiland Jordan, reporting from New York, said the "very strong statement" by the US ambassador had surprised many.

"Fayyad is universally liked by many diplomats here at the UN, so there was a real sense that the letter coming from Guterres was nothing more than a formality and that his appointment would be announced as early as next week."

Palestine is a non-member observer state at the UN and its independence has been recognised by 137 of the 193 UN member nations.

Haley, though, said the US does not recognise a Palestinian state "or support the signal" Fayyad's appointment would send.

Speaking from Ramallah, Hanan Ashrawi, senior member of the Palestine Liberation Organization (PLO), dismissed Haley's statement as "absolutely ridiculous", adding "there is no logic" that can explain the US position on Fayyad.

"This is discrimination against the Palestinian people as a whole," she told Al Jazeera. "This is the rejection, beyond logic, of the most qualified person with the highest standard of profession and integrity.

"It sets a precedent of excluding Palestinians from participation in the international arena, and depriving the international community from the skills and abilities, on the basis of national identity."

In an interview with Al Jazeera, Ali Abunimah, cofounder of the Palestine-focused Electronic Intifada website, called the US move "bizarre".

"It is ironic because Fayyad was elevated by the Bush administration to the Palestinian Authority," he said.

Abunimah said Fayyad's planned appointment to the post "had nothing to do with Palestine, the Palestinian Authority or Israel".

Difficult discussions

UN diplomats, speaking on condition of anonymity, told the Associated Press news agency that Fayyad was well-respected for his work in reforming the Palestinian Authority and revitalising the Palestinian economy.

Officials said Fayyad had the support of all 14 other Security Council members to succeed Martin Kobler, a German career diplomat who has served as the UN's Libya envoy since late 2015.

The US protest came days before a planned meeting between Israeli Prime Minister Benjamin Netanyahu and President Donald Trump at the White House on February 15.

"This is the beginning of a new era at the UN, an era where the US stands firmly behind Israel against any and all attempts to harm the Jewish State," Israel's UN Ambassador Danny Danon said of the US decision.

Trump, though, indicated in comments to an Israeli newspaper on Friday that there may still be difficult discussions with Netanyahu next week on Israel's settlement expansion.

The US president was quoted as saying that the expansion of illegal Israeli settlements did not help peace prospects.

Israel's settlements in Gaza, the West Bank and East Jerusalem, have been declared illegal by the UN, and have been a stumbling block in talks.