Hollywood star turned politician Arnold Schwarzenegger has hailed the "true action heroes" during a visit to British troops near Buckingham Palace.
He told the 1st Battalion the Grenadier Guards: "I know the difference between a movie action hero who is make-believe and the true action heroes.
"You all are the true action heroes because you are risking your life."
He was speaking after talks in Downing Street with UK Prime Minister David Cameron.
Those talks covered a range of subjects, including their respective efforts to tackle deficits.
Mr Cameron joked, as he posed for photos with the governor of California on the steps of Number 10, that he was there to help "terminate the budget deficit".
Mr Schwarzenegger watched the changing of the guard as well as visiting the soldiers at Wellington Barracks near Buckingham Palace.
The Austrian-born star - a former Mr Universe known for action films including The Terminator and Total Recall - has been Californian governor since 2003.
'In really great shape'
He told the troops: "I get hailed a lot of times when I travel around the world as being the action hero but.. you are risking your life every day when you go out to the front so I say thank you, thank you, thank you for the great work that you are doing."
"It's because you, for hundreds of years, have fought for the freedom, to keep these countries free and to keep these countries strong and to have the freedom of speech. Many countries in the world don't have that."
Mr Schwarzenegger also visited the gym, saying: "I was amazed when I saw your guys pumping up in the gym with those deltoids and those biceps and the six-pack. Wow, you guys are really in great shape."
He said he also went to the rehabilitation centre where he saluted those going "through this pain and torture and through the rehabilitation training... this is the kind of strength I see in each and every one of you when I look in your eyes".
Mr Cameron said the men had a "very tough tour" in Afghanistan but faced it with "incredible bravery and dedication".
He continued: "We are not in Afghanistan to build the perfect democracy. We will never leave behind a sort of Switzerland in the Hindu Kush but we can make that country safe from terrorist training camps, which will make us safe back here at home.
"I think the British public understand that and I think we have the strength of character to see this through and to see it through successfully."
He said he wanted to "celebrate the incredibly close relationship between Britain and America".
The governor and the prime minister have struck up a friendship in recent years as conservatives with a shared interest in environmental issues. Mr Cameron visited Mr Schwarzenegger in California in 2007.
And the governor was reportedly among the first to congratulate him when the general election results began coming in on 6 May, with what turned out to be a somewhat premature phone call shortly after polls closed at 2200BST.
It is not the star's first visit to Downing Street - he was a guest of Tony Blair's on 26 June 2007, Mr Blair's last full day as prime minister.
And he is not the only famous face at Number 10 on Thursday - former prime minister Baroness Thatcher will be paying a visit, for celebrations to mark her 85th birthday, along with 150 friends and colleagues.
The top US general in Afghanistan, General David Petraeus, is meanwhile due to hold talks with Mr Cameron later. They are expected to discuss the strategic defence review and the death of kidnapped British aid worker Linda Norgrove during a US rescue attempt.