British Jackie Cobell and Argentine Matias Ola swam across the Strait of San Carlos joining the Falkland Islands (Islas Malvinas) from west to east, as the UK defence secretary is expected to announce reinforcements of troops and equipment after Argentina is said to be buying long-range bombers from Russia.
Britain is to "beef up" the defence of the islands, the government confirmed on Tuesday 24 March, amid reports of an increased risk of invasion by Argentina.
Defence Secretary Michael Fallon is expected to announce reinforcements of troops and equipment in Parliament later on Tuesday after a defence ministry review suggested an attack on the south Atlantic archipelago was more likely.
When Fallon was asked whether the threat to the Falklands had increased following reports that Argentina was planning to lease 12 long-range bombers from Russia, he said the deal had not been confirmed, but the "threat remains".
A message of peace
The idea behind the swim was to send "a message of peace, friendship and harmony in memory of the fallen, considering that is not worthy to keep sowing enmity", the pair, who covered the 6km (4.2 miles) strait in 2.30 hours, wrote on their Twitter accounts.
The Strait of San Carlos, or Falkland Sound, is a symbolic place which was the scene of clashes between British ships and Argentine aircraft during the war of 1982.
The crossing took place on Friday night (20 March) without wetsuits and "without political flags without boundaries, spreading peace, unity and joy in every stroke", wrote Ola.
The 30-year-old Argentine activist described the event as "very extreme swimming with waves of over two metres at times, but thanks to teamwork we made a perfect journey".
Cobell, 60, is famous for having swum the English Channel for almost 29 hours, and holds the world record of the athlete who stayed the longest in the water and managed to cross the channel individually.