The US believes the UN Secretary General is too willing to accommodate Russian interests, according to fresh revelations in classified documents leaked online.

The files suggest Washington has been closely monitoring Antonio Guterres.

Several documents describe private communications involving 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 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 Guterres was so keen to preserve the deal that he was willing to accommodate Russia's interests.

His actions in February, according to the assessment, were "undermining broader efforts to hold Moscow accountable for its actions in Ukraine."

Russia has frequently complained that its own exports of grain and fertiliser are being adversely affected by international sanctions, and has threatened at least twice to suspend co-operation with the grain deal unless its concerns are addressed.