A Frenchman arrested in Bulgaria on January 1 trying to cross into Turkey was in contact with one of the two brothers who carried out the Islamist attacks in Paris last week, prosecutors say.

Fritz-Joly Joachin, 29, a French citizen of Haitian origin, “was in contact several times with one of the two brothers, Cherif Kouachi,” public prosecutor Darina Slavova said.

She said these contacts took place before Mr Joachin left France on December 30, a week before Cherif Kouachi and his brother Said killed 12 people in Paris attacks that shocked the world.

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Mr Joachin was initially detained on a European arrest warrant issued by France following allegations by his wife that he had kidnapped their three-year-old son.

But on Monday, as French police delved into the contacts of the Kouachi brothers, Bulgarian prosecutors received a second European arrest warrant issued by a court in Paris.

“The charges are for participation in an organised crime group whose aim was the organisation of terrorist acts,” Ms Slavova said.

The Kouachi brothers carried out their massacre at the Paris offices of French satirical weekly Charlie Hebdo on January 7. Two days later they were shot dead by French security forces.

Paris shooting gunman Amedy Coulibaly in the video posted on Twitter.

Separately Amedy Coulibaly, who had links to the brothers, shot dead a policewoman on January 8 and the next day four Jews in a kosher supermarket in Paris before also being killed by police.

According to Mr Joachin’s wife, Mr Joachin converted to Islam 15 years ago and turned radical two years ago. She said he planned to take their child to Syria to educate him in a jihadist community.

Mr Joachin told prosecutors however that he was travelling with his son and girlfriend just for a holiday in Istanbul, and Bulgarian media quoted him as denying being an extremist.

“I am Muslim but I am not a radical or terrorist,” the Presa newspaper quoted him as saying.

An extradition hearing is due to take place on Friday. On Monday he had said he would not contest his extradition back to France.

Bulgarian interior minister Veselin Vuchkov said that European Union (EU) citizens can easily cross over Bulgaria’s border into Turkey, and then into Syria to join Islamic State (IS) militants, if Bulgarian authorities are not alerted by their home countries.

“Many hundreds of citizens of the EU, with absolutely valid documents and without any security alerts about them, can easily cross Bulgaria’s territory,” he said.

Meanwhile, it was revealed that Coulibaly has been on a US terror watchlist “for a while”, a law enforcement official told CNN.

The US network said Coulibaly was on the Terrorist Identities Datamart Environment, the government’s central repository that includes about one million names.

In a video posted online on Sunday, a man identifying himself as Coulibaly claims responsibility for the Montrouge attack in the name of the Islamic State group, and says he “co-ordinated” his actions with the Kouachi brothers.

The bodies of the four French Jews killed by Coulibaly at the kosher supermarket – Yoav Hattab, Philippe Braham, Yohan Cohen and Francois-Michel Saada – were on their way to Israel early on Tuesday ahead of a funeral in Jerusalem.