In the UK, Ukip leader Nigel Farage said the attack on Charlie Hebdo was "truly horrific," adding that it raised questions about what he called a "gross policy of multiculturalism".
Farage told British news network Channel 4 News there was a "very strong argument" that the events were a result of "a fifth column" which he said lived in Paris and London.
"We've got people living in these countries, holding our passports, who hate us," he said.
The leader of the UK's junior coalition party the Liberal Democrats was among the most vocal critics of his comments. Nick Clegg stated on a radio phone-in that he was "dismayed that Nigel Farage immediately thinks, on the back of the bloody murders that we saw on the streets of Paris…his first reflex is to make political points."
In France, a huge row broke out on Thursday after the National Front party was not invited to a rally to remember the Paris shooting victims on Sunday.
Former French Prime Minister François Fillon said: “"Our best response is the total unity of the country. We can't have any dissenting voices.”
“It’s a mistake, we should unite everyone and not judge people by their political colours,” Imam Farid Darrouf told The Guardian newspaper.
“Everyone should participate to say no to this barbarism. Division can only feed the fanatics.”