Russia's Defence Ministry said on Wednesday that "Ukrainian saboteurs" had blown up a section of the Togliatti-Odesa ammonia pipeline that carries fertiliser from Russia to Ukraine in Kharkiv region on Monday.

The ministry said it would take up to three months to repair the pipeline.

The statement follows reports from Ukraine that Russian forces had repeatedly fired at the pipeline.

What does the pipeline carry?

Russia uses the pipeline to pump up to 2.5 million tonnes of ammonia annually for global export to Ukraine's Pivdennyi port on the Black Sea from Togliatti on the Volga River in western Russia. It has been shut down since Moscow's invasion of Ukraine.

It is the world's longest ammonia pipeline at about 2,470km in length, the International Energy Agency says.

What does it mean for the Black Sea grains deal?

The United Nations and Turkey brokered the Black Sea Grain Initiative for an initial 120 days last July to help tackle a global food crisis worsened by Moscow's invasion of Ukraine, one of the world's leading grain exporters. It has been extended three times since, most recently until July 17.

More than 31 million tonnes of mostly corn and wheat have been exported by Ukraine under the deal. The Black Sea Grain Initiative also allows for the safe export of ammonia - an ingredient of nitrate fertiliser - but none has been shipped.

Extending the grains deal to allow the safe wartime export of grains and fertilisers from three Ukrainian Black Sea ports is likely to more difficult if the pipeline is damaged, given that Russia has repeatedly demanded during negotiations that its ammonia exports should be facilitated.

What had Russia demanded?

Moscow previously said it was "ready without delay, in a matter of days" to restart the ammonia pipeline. Now it says it will take up to three months to repair it.

Until the ammonia pipeline can be restarted, Moscow has said it will limit the number of vessels allowed to travel to Pivdennyi port under the Black Sea deal, the United Nations said.

UN data shows no ships have visited Pivdennyi port for more than three weeks.

Under the Black Sea Grain Initiative, a joint coordination centre in Istanbul made up of officials from Ukraine, Russia, Turkey and the UN agrees on the ships to be registered and conducts inbound and outbound inspections in Turkish waters.

How has Ukraine responded?

The Black Sea Grain Initiative covers the "safe navigation for the export of grain and related foodstuffs and fertilisers, including ammonia" from the Ukrainian Black Sea ports of Odesa, Chornomorsk and Pivdennyi, known in Russian as Yuzhny.

Ukraine has said the language of the deal does not cover the transit of Russian ammonia across Ukraine. A Ukrainian government source told Reuters that Kyiv would consider restarting the pipeline in exchange for an expansion of the Black Sea grain deal to include more ports and commodities.

Russia had said the transit of ammonia "although not spelled out literally, is implied by the logic of the agreement".

UN proposal to restart ammonia pipeline

In September, Reuters reported that the United Nations proposed that ammonia gas owned by Russian fertiliser producer Uralchem be brought via pipeline to the Russia-Ukraine border.

At the border it would be purchased by US-headquartered commodities trader Trammo, according to the proposal. Trammo has been approached by the United Nations to assist in this project and is happy to cooperate, it said in an emailed statement.

The United Nations has consistently pushed for the reopening of the ammonia pipeline.

Reuters reported last week that the US proposed that Kyiv, Moscow and Ankara begin preparatory work on restarting the pipeline, while conducting parallel talks to broaden the Black Sea deal to include more Ukrainian ports and other cargoes.