Watch: Sam Heughan discusses physicality of SAS: Red Notice
Sam Heughan has described a "visceral" fight scene in a snow-dusted forest as his proudest action moment in new thriller SAS: Red Notice.
The 40-year-old Outlander star has an extended fistfight with Ruby Rose during the movie, in which he plays a Special Forces operative who fights back when Rose's mercenary boss hijacks a train in the Channel Tunnel.
Directed by Magnus Martens, the movie is based on a novel by former soldier turned author Andy McNab.
Read more: Heughan reveals he wants to be James Bond
Heughan tells Yahoo Entertainment UK that SAS was a physical shoot and that he wishes to thank the "brilliant stunt team" who assisted him in getting the fights in the can.
He says: "I think luckily I'd just come from shooting Bloodshot in South Africa with Vin Diesel and that was a very physical movie and obviously on Outlander I do a lot of physical stuff as well, so I have a good understanding of action, which was great.
"I did do a lot of work with Special Forces, learning to move tactically, and then with Andy McNab himself doing more the psychology and tactics behind how the military operates.
"There were some new skills learned for this job, but also I could use some of the ones I'd learned before as well."
But it's the brutal fight with Rose that Heughan really enjoyed shooting, which serves as the culmination for a movie with more than its fair share of bloodletting.
"I think it just looks incredible," he says. "We trained hard for that one and we wanted to make it really visceral.
"And also using these martial arts, this way of fighting the military has which is just so effectual. It really is just like: what is the quickest, most effectual way of stopping someone?
"It was a brutal fight, literally just using their bodies, throwing each other at themselves. I think it turned out really well."
Read more: Rose reveals reason for Batwoman exit
Heughan says the movie benefited from Rose's experience with big screen and small screen action, from her work in John Wick: Chapter Two and as the title character in the Batwoman TV show.
"She really jumped in. She wanted to do as much as she could," he says.
"We also looked at it from a character perspective. She's smaller than I am. She's not as strong. How does someone like that prove a challenge for someone like my character?
"But she really is. She's ruthless, she just uses her body, she throws herself at him.
"We talked about it like she's a small dog, which just goes for a larger one and is aggressive. She will not stop. She's relentless and that's what makes her such a terrifying adversary.
"Add to that the fact that she's a psychopath as well, which means there's zero empathy, but great intelligence there."
Read more: Tom Cruise and dangerous movie stunts
The rest of the movie's ensemble is a terrific array of British talent, including Hannah John-Kamen, Andy Serkis, Noel Clarke and Tom Wilkinson.
SAS: Red Notice is available to stream via Sky Cinema and NOW TV from 12 March.
Watch: Trailer for SAS: Red Notice