Global outrage and offers of assistance poured in after French police killed Islamist gunmen in two sieges in the Paris region.

The horror was so universal that even foes of the west North Korea and Cuba sent condolences, while bitter enemies Israel and Iran were at least united in their condemnation of the slaughter.

The latest attacks prompted vigils in several cities around the world to declare "Je suis Charlie" in a show of support for free speech.

Prime ministers David Cameron and Mariano Rajoy of Britain and Spain, whose countries have suffered major terror attacks in the past decade, were among the first to say they would attend.

Cameron said Sunday's rally would be celebrate "the values behind Charlie Hebdo".

The leaders of Germany, Italy, Belgium, Portugal, Poland, Sweden, Denmark, Norway and Ukraine also said they would attend.

European Council President Donald Tusk and European Commission chief Jean-Claude Juncker said they would attend the Paris rally as well, accompanied by EU foreign affairs chief Federica Mogherini.

The global reaction in some ways mirrors the outpouring of support after the September 11, 2001 attacks in the United States, when French newspaper "Le Monde" announced on its front page "Today, we are all Americans."

World leaders condemned the 9/11 attacks and offered aid, while mourners piled flowers at US embassies and Buckingham Palace played the US national anthem at the changing of the guard.

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