The US believes the UN Secretary General is too willing to accommodate Russian interests, according to fresh revelations in classified documents leaked online, the BBC reports.
The files suggest Washington has been closely monitoring Antonio Guterres.
Several documents describe private communications involving Mr Guterres and his deputy.
It is the latest from a leak of secret documents, which US officials are scrambling to get to the bottom of.
The documents contain candid observations from Mr Guterres about the war in Ukraine and a number of African leaders.
One leaked document focuses on the Black Sea grain deal, brokered by the UN and Turkey in July following fears of a global food crisis.
It suggests that Mr Guterres was so keen to preserve the deal that he was willing to accommodate Russia’s interests.
“Guterres emphasised his efforts to improve Russia’s ability to export,” the document says, “even if that involves sanctioned Russian entities or individuals.”
His actions in February, according to the assessment, were “undermining broader efforts to hold Moscow accountable for its actions in Ukraine.”
UN officials bristled at the suggestion that the world’s top diplomat was being soft on Moscow.
Saying he wouldn’t comment on leaked documents, one senior official said the UN was “driven by the need to mitigate the impact of the war on the world’s poorest.”
