Moscow: Russian Foreign Minister Sergei Lavrov said Thursday that extending a deal that allowed grain exports from Ukraine to resume was becoming "complicated" as he claimed it was not being properly implemented.

Russia's military intervention last February saw Ukraine's Black Sea ports blocked by warships until a deal last summer allowed for the safe passage of exports of critical grain supplies.

The UN and Turkey-brokered deal will automatically renew on March 18 unless Moscow or Kyiv object.

But Lavrov said clauses in the agreement that provide for Russian grain and fertiliser exports were not being upheld.

"If the package is half fulfilled, then the issue of extension becomes quite complicated," he said during a press conference with his Saudi counterpart in Moscow.

On Tuesday UN chief Antonio Guterres said it was crucial to extend the deal in a visit to Kyiv.

His call followed a statement last week from US Secretary of State Antony Blinken at a Group of 20 meeting, who demanded that Moscow renew the agreement.

But Russia, who was promised under the deal the right to export fertiliser free from Western sanctions, claims that part of the agreement is not respected.

"Our Western colleagues, the United States and the European Union, pathetically declare... that no sanctions apply to food and fertilisers, but this position is dishonest," Lavrov said.

"In fact the sanctions prohibit Russian ships carrying grain and fertilisers from entering the corresponding ports, sanctions prohibit foreign ships from entering Russian ports to pick up this cargo," he said.