All 100 US senators have signed a letter to United Nations Secretary-General António Guterres to address the “unacceptable” anti-Israel bias at the international body.

The letter, which singled out the United Nations Relief and Works Agency (UNRWA) and UNESCO for criticism, was written by Florida Republican Marco Rubio and Delaware Democrat Chris Coons and signed by every member of the upper house this week.

It read: “Through words and actions, we urge you to ensure that Israel is treated neither better nor worse than any other UN member in good standing.

“As both the UN’s principal founding member and its largest contributor, the United States should insist on reform.

“We are deeply committed to international leadership and to advancing respect for human rights. But continued targeting of Israel by the UN Human Rights Council and other UN entities is unacceptable.”

The letter also called on the UN to abolish or reform a number of standing committees, which senators said “far too often serve no purpose other than to attack Israel and inspire the anti-Israel boycott, sanctions and divestment (BDS) movement.”

Although UNESCO was praised for its work on Holocaust education, the letter criticised it for allowing member states to “deny the Jewish and Christian connections to Jerusalem”.

It also criticised UNRWA, which works with Palestinian refugees. In the past Israeli officials have accused the organisation of collusion with Hamas. More than one third of UNRWA’s budget comes from the United States.

The US has long been the prime defender of Israel at the UN. In February US President Donald Trump said he rejected the “unfair and one-sided” actions against Israel by the UN.

A month later US ambassador to the UN Nikki Haley said the days of “Israel-bashing” were over, declaring there to be a “new sheriff in town”.