The deaths were reportedly the result of a vehicle ploughing into pedestrians on Westminster Bridge near the Houses of Parliament in central London.
Around 40 people were reported as injured in what appeared to be a deliberate attempt to kill and maim as many as possible.
Police have yet to confirm the identity of the attacker or attackers, not have they established a motive, despite inevitable widespread speculation and guesswork on social and mainstream media.
President Raimonds Vejonis said the incident provided a reminder of "our common pledge to fight terrorism."
#Westminster reminds again our common pledge to fight terrorism.— Valsts prezidents (@Rigas_pils) March 22, 2017
Prime Minister Maris Kucinskis said he "strongly condemned" what he called a terrorist attack.
Strongly condemn terrorist attack at #Westminster. Wish quick recovery to the injured!— Maris Kucinskis (@MarisKucinskis) March 22, 2017
So did Foreign Minister Edgars Rinkevics, currently in the US:
I express Latvia's full solidarity & support to our strong ally UK over terrible terrorist attack in London, condolences to all affected ??— Edgars Rinkēvičs (@edgarsrinkevics) March 22, 2017
Latvia's embassy in the UK immediately swung into action as news of the incident broke, encouraging Latvians in the UK to tell families back home they were safe and also urging anyone with information relevant to the incident to contact police.
The embassy also offered thanks to the Metropolitan Police "for keeping us safe".