Boris Johnson has served Christmas lunch to British troops during a visit to a Nato mission in Estonia.
Visiting the Tapa military base near Tallinn, Mr Johnson wished them a merry Christmas as he dished up the meals.
The 850 British soldiers based there represent the UK's largest operational deployment in Europe.
The PM also stressed the UK's commitment to Nato and its defence of Estonia's eastern border with Russia.
The UK is playing a leading role in the alliance's Baltic mission.
The troops, from the Queen's Royal Hussars, head the Nato battle group in Estonia, working alongside the country's troops and personnel from France and Denmark.
Mr Johnson told them: "In the course of the next few days, everybody in our country is going to be celebrating Christmas with their families and you're going to be here - a long way away, a pretty cold place.
"What you're doing is incredibly important because the reason everybody in our country can have Christmas in peace and security is because of what you're doing here.
"What you're doing is showing that Nato works and that Nato is an alliance to which we in this country are absolutely committed to."
Downing Street said Mr Johnson also held talks with Estonian Prime Minister Juri Ratas and thanked him for the "support and hospitality Estonia has shown in hosting British Armed Forces".
The No 10 spokeswoman added: "The leaders discussed the close partnership between the UK and Estonia, in particular our joint security and defence cooperation. The prime minister reaffirmed the UK's unconditional commitment to Estonia's regional security through Nato.
"The two leaders discussed the need to work together to address shared global challenges and the prime minister invited Prime Minister Ratas to attend the COP26 climate change summit in Glasgow next year."
During a four-month deployment earlier this year, a squadron of RAF Typhoon jets was scrambled 21 times to intercept 56 Russian aircraft which had strayed over the border into Estonian airspace.
The UK is one of the few Nato countries that meets the commitment to spend at least 2% of national income on defence.
The armed forces were given an extra £2.2bn in September's spending review when Chancellor Sajid Javid announced a 2.6% increase in defence funding in 2020-1.
But a prolonged squeeze on defence spending between 2010 and 2015 has prompted questions about whether the UK is adequately equipped to meet future security threats.
In February, the Public Accounts Committee, the House of Commons' spending watchdog, reported that the MoD faced a £7bn black hole in its 10-year-plan to equip the armed forces.
In a BBC interview on Thursday, Defence Secretary Ben Wallace said there was a shortfall of funding in the MoD's budget and confirmed he had recently met with Mr Johnson's chief adviser Dominic Cummings about improving the way the department spends its money.