The United States has blocked the appointment of former Palestinian prime minister Salam Fayyad to lead the United Nations' political mission in Libya, saying it was acting to support its ally Israel.
US ambassador to the UN Nikki Haley said the Trump administration "was disappointed" to see that UN secretary general Antonio Guterres had sent a letter to the world body's Security Council indicating his intention to appoint Mr Fayyad, who was the Palestinian Authority's prime minister from 2007-2013, as the next special representative to Libya.
"For too long the UN has been unfairly biased in favour of the Palestinian Authority to the detriment of our allies in Israel," Ms Haley said.
Palestine is a non-member observer state at the UN and its independence has been recognised by 137 of the 193 member nations.
But Ms Haley said the United States did not currently recognise a Palestinian state "or support the signal" Mr Fayyad's appointment would send within the UN.
UN diplomats said Mr Fayyad was well-respected for his work in reforming the Palestinian Authority and spurring its economy and had the support of the 14 other Security Council members to succeed Martin Kobler in the Libya job.
Despite opposition to Mr Fayyad, Ms Haley indicated that the Trump administration wanted to see an end to the decades-old Israeli-Palestinian conflict.
"We encourage the two sides to come together directly on a solution," she said.
Her statement came ahead of Israeli prime minister Benjamin Netanyahu's meeting at the White House with US president Donald Trump on February 15, and was welcomed by Israelis.
"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 to block Mr Fayyad's appointment.
"The new administration proved once again that it stands firmly alongside the state of Israel in the international arena and in the UN in particular."
The new US ambassador made clear that "going forward, the United States will act, not just talk, in support of our allies".
But Mr Trump also indicated in comments to an Israeli newspaper on Friday that there might be some difficult discussions with Mr Netanyahu next week on Israel's settlement expansion.
Mr Trump was quoted as saying that Israel's settlement expansion in land claimed by the Palestinians does not advance peace.
Israel's settlement building has been a key obstacle to the revival of stalled peace talks between Israel and the Palestinians.
Most of the international community considers all Israeli settlements in territory the Palestinians want for a state in Gaza, the West Bank and East Jerusalem illegal and counter-productive to peace.