Fighters on Ukraine's front line may have a very up-to-date kind of backing.

A new report Tuesday (February 8) showed large sums of bitcoin flowing to volunteer groups.

Blockchain researcher Elliptic says around $550,000 of cryptocurrency was donated last year.

Some of the recipient groups have used that to buy equipment for government forces.

They're preparing for a possible Russian attack, though Moscow denies having any plan to invade.

Cryptocurrencies can be sent and received anonymously, allowing transactions to skirt any restrictions.

In Ukraine cross-border transfers of cash are subject to mandatory monitoring as part of moves to tackle money laundering.

Elliptic says one organisation called Come Back Alive received $200,000 in crypto in the second half of last year.

The Ukraine-based group buys gear for Ukraine's army including drones and sniper-rifle scopes.

Come Back Alive did not respond to a request for comment on the report.

Another group called the Ukrainian Cyber Alliance is said to have received about $100,000, though it denies getting anything like that sum.

In comments last year the Alliance said it aimed to pass information on Russian political and security figures to the Ukrainian military.

Reuters hasn't been able to independently verify the sums detailed in the report.