A third man has been detained for questioning in connection with the knife attack on a church in the southern French city of Nice which left three people dead, a legal source said Saturday.

The man, 33, was present during a police search late Friday at the home of a second man suspected of having been in contact with the attacker, a young Tunisian, the source said.

"We are tyring to clarify what his role is in all this," the source added.