The Russian military has been accused of offering bounties to Taliban-linked gunmen to kill British and US soldiers in Afghanistan.
Bounties were said to have been offered by Unit 29155 of Russia's GRU military intelligence agency, the same unit blamed for the nerve agent attack on former Russian spy Sergei Skripal in Salisbury in 2018.
US intelligence officials have briefed Donald Trump on the development and the British government was alerted this week, the New York Times reported.
The alleged escalation by Russia first emerged in March but the US has not yet responded, although sanctions were reportedly under consideration.
The UK ceased combat operations in Afghanistan in 2014 but still has 1,000 troops in the country, working with Afghan forces and providing force protection for Nato.
Last year 20 Americans were killed in combat in Afghanistan. Another four died this year. US troops have been moving around less recently due to the coronavirus.
It was not clear which US deaths were under suspicion of being linked to Russian bounties.
Islamist militants, or armed criminal elements closely associated with them, were believed to have collected some bounty money, according to the New York Times.
Russia's alleged encouragement of the targeting of US and coalition troops appeared to have aimed at keeping America bogged down, prolonging its longest war as Mr Trump tried to withdraw.
It was also possible the Russian military was responding to the US killing of Russian mercenaries during a battle in Syria, where Moscow backs Bashar al-Assad, in 2018.
Russia has also been accused by the US of quietly providing small arms to the Taliban, which Russia has denied.
The latest intelligence of escalated Russian involvement reportedly originated from interrogations of captured Afghans.
White House officials, the CIA, and the Pentagon declined to comment on the reports of Russian bounties. The UK Foreign Office also declined to comment.
US intelligence officials were said to be unsure at what level the Russian move was authorised. Russia's foreign ministry called the allegations "nonsense".
A spokesman said: "What else can be expected from [US] intelligence, which miserably failed the twenty-year war in Afghanistan?"
Taliban spokesman Zabihullah Mujahid said: "We categorically reject the notion of ever planning or carrying out targeted attacks against US or foreign forces at the behest of foreign intelligence or for the sake of collecting bounty."
On Feb 29 the US and the Taliban struck a deal that called for a phased troop withdrawal.
US troop strength in Afghanistan is down to nearly 8,600, well ahead of a schedule agreed with the Taliban, in part because of concerns about the spread of the coronavirus.
Democrats seized on the reported Russian escalation to accuse Mr Trump of failing to stand up to Russia.
Tim Kaine, Hillary Clinton’s running mate in 2016, said: "Trump was cosying up to Putin and inviting him to the G7 all while his administration reportedly knew Russia was trying to kill US troops in Afghanistan and derail peace talks with the Taliban."