Hundreds of people queued from the early hours outside UK shops selling the latest edition of French satirical magazine Charlie Hebdo.
It comes as around 10 people have been arrested and questioned over the "possible logistical support" they may have provided three gunmen who carried out last week's attacks in Paris, Agence France-Presse reports.
Footage and intelligence from this morning's Charlie Hebdo shooting indicates that the attackers were "well trained" killers, a terror expert has said.
Claude Moniquet, co-director at the European Strategic Intelligence and Security Center, said that using a weapon to deal with the "stress" of killing on a large scale required training, probably in "real conditions", such as the war in Syria.
"In the past we had a few hundred dangerous people in all Europe. Today, we have at least a few hundred dangerous people in each European country," he added.
About 7,000 French Jewish people left the country last year and have moved to Israel because they did not feel safe.
The aunt of a man killed while trying to overpower gunman Amedy Coulibaly has told ITV News her family is fearful of their future in France.
A Muslim cleric in Pakistan has held a ceremony to honour Cherif and Said Kouachi, the two men suspected of the Charlie Hebdo massacre.