Britain was informed of Russian efforts to win Mauritian officials' backing for a Chagos Islands claim.
According to the DailyMail, during negotiations, government ministers were told Vladimir Putin's staff tried to "undermine UK interests" by promoting Mauritian claims to the Chagos Islands.
A former Whitehall official told The Telegraph that Russia is "actively prompting" the argument for "Mauritian sovereignty" to weaken the UK.
However, the source said government officials ignored the warnings.
"It is absolutely extraordinary that the Government has not taken two and two and made a very obvious four," they said.
The Foreign Office claimed it was "well aware" of "malign actors"' methods in the Chagos transaction but considered them while negotiating.
Sir Keir Starmer wants Mauritius to take up the Chagos Islands before Trump takes office.
Under the accord, the UK would relinquish more than 60 islands, including Diego Garcia, the military station, and the surrounding waters.
The pact needs US backing since Diego Garcia, the most oversized island in the British Indian Ocean Territory, is home to a joint US-UK military station.
Meanwhile, the newly-elected Prime Minister of Mauritius has ordered a review of the new agreement signed by his predecessor.
Mr. Ramgoolam and his followers called the accord a "sell-out" out of desperation and accused then Prime Minister Pravind Jugnauth of "high treason."
Mr. Ramgoolam "would like to have more time to study all the details of the agreement with a panel of legal advisers" and requested an independent assessment of the private draft agreement with Britain.
The Telegraph quoted RUSI senior research fellow for European security Ed Arnold as saying, "the worry is that this deal benefits China so in this case it might be that the Kremlin is actually doing Beijing a favor by acting on their behalf."
This week, former PM Boris Johnson called ceding sovereignty of the Chagos Islands "spectacularly shooting ourselves in the foot."
"It's driven by pure Lefty politics and it's a tragedy that Starmer has bought into this nonsense," he told a podcast. "I don't know what the Trump administration will do with it now, but perhaps they will find a way of impeding it."
Foreign Secretary David Lammy called Labour's deal to cede sovereignty of the Chagos Islands to Mauritius "politicking" this week.
He called the sovereignty treaty a "very good deal" and denied it was about to collapse.
Mr. Lammy downplayed mounting criticism of the accord to the House of Commons foreign affairs committee.
"I'm very, very confident that this is a deal that the Mauritians will see, in a cross-party sense, as a good deal for them," the Foreign Secretary said.
Reactions on social media indicate polarized viewpoints.
"If true, Russia's interference is outrageous. The UK should've acted decisively," one netizen wrote.
"Boris calling this leftist politics? It's about justice, not ideology," a second said.
"Diego Garcia's strategic importance can't be overstated-this deal risks too much!" a third chimed in.
"Starmer's decision to pursue this now is irresponsible with Trump coming in," a fourth netizen said.
"Mauritius deserves sovereignty, but this interference muddies the waters," a fifth netizen wrote.
"America must tread carefully-China and Russia are circling the Indian Ocean," another said.
Business Times has reached out to Donald Trump for comments.
