SOFIA (Reuters) - Bulgaria plans to extradite a Frenchman suspected of knowing or having been in touch with one of the two Islamist militants who shot dead 12 people at the satirical newspaper Charlie Hebdo's offices last week, prosecutors said on Monday.

Using a European arrest warrant alleging that he had abducted his 3-year-old son and was likely to take him to Syria, Bulgarian police arrested Fritz-Joly Joachin, 29, on Jan. 1 at a border checkpoint when he tried to cross into Turkey.

A second European arrest warrant cites his possible association with one of the attackers and "conspiracy in terrorism" but has not yet been officially translated, a spokesman for the Haskovo regional prosecutors' office said.

The chief prosecutors' office in the Bulgarian capital Sofia confirmed that the second warrant was issued on the grounds that Joachin was part of a criminal group planning terrorist acts.

The man has agreed to be sent back to France and a Haskovo court will make a final decision on the extradition on Friday, one prosecutor said.

According to the initial arrest warrant, Joachin's wife told authorities on Dec. 30 that he was likely to take their son to Syria, that he had converted to Islam 15 years ago and had become radicalized in recent years.

France said it will mobilize 10,000 soldiers by Tuesday and its defense minister said the country remained at risk of further attacks.