The United States is working with the United Nations to address Russian complaints that sanctions are hindering its food and fertiliser shipments, even though there has been no disruption to Moscow's exports of the commodities, Reuters reported, citing a senior US official on Friday.

The United Nations, Turkey, Ukraine and Russia agreed on July 22 on what was described by UN chief Antonio Guterres as a package deal to restart Ukraine's Black Sea grain and fertiliser exports and facilitate Russian shipments.

"We're seeing no disruption in Russia's ability to send food to market," James O'Brien, head of the State Department's Office of Sanctions Coordination, told reporters. "The fertiliser is still reaching markets at the same rate that it always has."

While the United States and others have stressed that Russian food and fertiliser is not subject to sanctions imposed over Moscow's February 24 invasion of its neighbor, Russia has asserted there has been a chilling effect on its exports.

"The complaints, I think, are just an example of misinformation," said O'Brien.

Washington was "working in good faith," O'Brien said but asserted that Russia does not need the deal because "it's got access to the markets through other means."

O'Brien said the United States would do "everything we can" to address specific complaints and "Russia and the UN are just now engaged on some specific requests that it has under the UN agreement and I think we'll see progress in that over the next few weeks."

Senior UN and Russian officials met in Geneva on Wednesday to discuss Russia's complaints. The United Nations described the discussions as positive and very constructive.

O'Brien said the United Nations had brokered a way for the United States to speak with some of the Russian companies about specific concerns.

"We will do what's needed to make clear to every commercial player that they are allowed to buy Russian food and fertiliser," he told reporters, adding that so far Washington only had to had to issue one so-called comfort letter to make clear a transaction was allowed.

Moscow says logistical sanctions and restrictions on Russian ships entering Western ports or securing insurance restrict Russia's access to world markets. It says easing these restrictions was part of the export deal.

Russian President Vladimir Putin criticized the deal on Wednesday, saying Ukraine was exporting food and fertiliser to the European Union and Turkey rather than to poor countries. The pact allowing Ukraine's exports is up for renewal in November.

The United Nations has said that 30% of the grain and other foodstuffs that had left Ukraine under the deal so far had gone to low and lower-middle income countries.