A 55-year-old man was killed at a panel discussion about Islam and free speech yesterday, and in a second attack, a young Jewish man was killed outside Copenhagen's main synagogue early today.
Cameron said the two victims had been "murdered simply for their beliefs".
"Denmark and Britain are both successful multi-ethnic, multi-faith democracies and we must never allow those values to be damaged by acts of violence like this," he added.
"We offer our full support for the Danish government and Danish people as they deal with these terrible incidents."