The bloodshed in France could signal the start of a wave of attacks in Europe, according to communications by Islamic State leaders intercepted by US intelligence, German newspaper Bild reported Sunday.
Meanwhile, a video shows terrorist Amedy Coulibaly swearing allegiance to the Islamic State group and its leader Abu Bakr al-Baghdadi prior to his attack on a kosher supermarket.
In the seven-minute video apparently intended for release after the actions, Amedy Coulibaly, who staged the attack on a Jewish deli, said the planned assaults on a satirical journal and a Jewish target were justified by French military interventions overseas.
A French anti-terrorist police source said there was no doubt it was Coulibaly in the French-language recording.
Coulibaly had also called BFM-TV on Friday to claim allegiance to Islamic State, saying he wanted to defend Palestinians and target Jews.
He said in that call that he had jointly planned the attacks with the Kouachi brothers. Police confirmed they were all members of the same Islamist cell in northern Paris.
The video showed scenes of man resembling Coulibaly doing physical training and images of an arsenal of weapons and ammunition on the wooden floor of an apartment. He was shown variously in white robes, sitting with a gun at his side, and in combat outfit.
"I pledged allegiance to the Caliph as soon as the caliphate was declared," he says, referring to Islamic State leader Abu Bakr al-Baghdadi, whose group is an anti-government paramilitary force in both Iraq and Syria that has a growing network of followers elsewhere in the Middle East and Asia.
Coulibaly said he would be working together with the Kouachi brothers: "We've done things a bit together, a bit apart, to try and (achieve) more impact."
French police were also put on high alert after intelligence learned that he could have activated sleeper cells in the nation.
Shortly after the attacks in Paris, the US National Security Agency (NSA) had intercepted communications in which leaders of the extremist group announced the next wave of attacks, the tabloid said, citing unnamed sources in the US intelligence services.
Paris was cited as being the signal for a series of attacks on other European cities, including Rome, the newspaper said, adding however, that a concrete plan of attack was not known.
The US services also had information that Cherif and Said Kouachi, the brothers who carried out the massacre at French satirical weekly Charlie Hebdo, had contacts in the Netherlands, Bild said.
Al Qaeda's branch in Yemen said it directed Wednesday's attack against the publication Charlie Hebdo to avenge the honor of the Prophet Muhammad, a frequent target of the weekly's satire.
Loyalists of al Qaeda and the Islamic State group extolled the attackers as "lions of the caliphate." They described the attack as revenge for the French satirical publication's mockery of Muhammad and for France's military involvement in Muslim countries.
That attack Wednesday was the first act in France's worst terrorist attacks in decades.
Seventeen people were killed in the attacks on the newspaper, a kosher supermarket in Paris and police. The three gunmen - the Kouachi brothers and Amedy Coulibaly - were killed by French police. Meanwhile, the search for Coulibaly's widow, Hayat Boumeddiene, is still ongoing.
"You must consider her as the companion of a dangerous terrorist who needs to be questioned," Christophe Crepin, spokesman for the US police union, told The Associated Press.
But reports later said she might have fled the country into Turkey where she is could be attempting to cross into Syria.