(Reuters) -A pipeline used to transport ammonia fertilizer from Russia via Ukraine that may be central to the future of the Black Sea grain deal has been damaged, according to both Kyiv and Moscow, potentially complicating talks around the accord.

Russia's defence ministry said a "Ukrainian sabotage group" had blown up a section of the pipeline on Monday night near the village of Masyutivka in Kharkiv region. The village is on the frontline between Russian and Ukrainian troops.

"As a result of this terrorist act, there were civilian casualties. They have been provided with necessary medical assistance," the Russian ministry said in a statement.

"At present ammonia residues are being blown out of the damaged sections of the pipeline from Ukrainian territory. There are no casualties among Russian servicemen."

Oleh Sinehubov, the governor of Ukraine's Kharkiv region gave a different version of events. He said in a statement posted on Telegram that Russian troops had shelled the pipeline.

Six Russian shells had landed near a pumping station near Masyutivka at around 5:45 p.m. (1445 GMT) on Tuesday, nearly 24 hours after Moscow alleged Ukraine had blown up the same pipeline, he said.

Reuters could not independently verify the Russian and Ukrainian assertions.

The Russian section of the pipeline is safe and under control, Russian agencies reported, citing the operating company.

"The Russian part of the ammonia pipeline, which belongs to Transammiak, is securely cut off from the Ukrainian part and is in a safe and serviceable condition under constant control," the Interfax news agency cited the company's press office as saying.

REPAIRS

Resumption of supplies via the Tolyatti-Odesa pipeline, the world's longest ammonia pipeline, may be key to the renewal of the Black Sea grain export deal. The pipeline has been closed since Russia invaded Ukraine in February 2022 in what it called a "special military operation".

Russia has repeatedly cast doubt on whether it will continue to renew the grain deal, brokered by the United Nations and Turkey, which facilitates agricultural exports from Ukraine via the Black Sea.

Among the conditions for renewal that Moscow has put forward is resumption of the Togliatti-Odesa pipeline.

The United Nations has not received any official notification about damage to the pipeline, U.N. spokesperson Stephane Dujarric said on Wednesday.

"Any threat to this pipeline is indeed of concern," Dujarric told reporters. "We're continuing to engage with the parties on the ammonia exports, regardless of what may have happened."

Moscow has said it will limit the number of ships allowed to travel to Ukraine's Pivdennyi port near Odesa under the deal until the pipeline is restarted.

In a briefing on Wednesday, Russian Foreign Ministry spokeswoman Maria Zakharova said it would take between one and three months to repair the damaged section of the pipeline.

"The ammonia pipeline was one of the linchpins of the implementation of the agreements made in Istanbul on July 22, The (pipeline) was key to global food security," Zakharova said.

(Reporting by Reuters; Writing by Felix Light/Andrew OsbornEditing by Jon Boyle, Jason Neely, Gareth Jones, Alex Richardson and Diane Craft)