The gunman who killed 39 people in a Tunisian beach hotel attack last week was in contact with militants in Libya and likely received training there, an official source said on Tuesday.
Saif Rezgui, disguised as a tourist, opened fire at the Imperial Marhaba hotel in the resort town of Sousse on Friday in the worst militant assault of its kind in modern Tunisian history. Most of the dead were British.
"Investigations show Saif Rezgui was in contact with terrorists in Libya and he likely trained in a Libyan camp," an official source told Reuters.
Rezgui was shot dead by police.
Tunisian authorities have arrested a group of suspects associated with him, the interior minister said on Monday without giving a number or details on links.
"Police arrested three Tunisians who were involved in planning the attack with Rezgui," the source said.
Libya, caught in a conflict between two rival governments, has become a haven for Islamist militants who have used the lack of security to extend their influence there.
Thousands of tourists have left Tunisia since Friday's attack, an economic blow to a country which that relies heavily on tourism for jobs and foreign currency revenues.