Tunisia's security forces have called on the government to adopt "exceptional measures" to deal with potential security threats from fighters who have returned to their home country.
On Friday evening, the country's interior minister, Hedi Majdoub, told parliament that 800 Tunisian nationals who had travelled abroad to fight for armed groups in other countries have since returned to Tunisia.
Tunisia has witnessed a wave of attacks since its 2011 revolution, including on foreign tourists, and the United Nations estimates that there are more than 5,000 Tunisians fighting for armed groups, mainly in Iraq and Syria.
"The return of terrorists from hotbeds of unrest in Tunisia is worrying and could lead to the Somalisation of the country," said a statement from the internal security forces' national union.
Fighters "have received military training and have learnt to use all sorts of sophisticated weapons", it added.
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The warning came a day after Tunisian authorities said they had arrested three people, including the nephew of Anis Amri, the 24-year-old suspected of carrying out a deadly truck attack on a Berlin Christmas market this week.
Hundreds of people gathered outside parliament in Tunis on Saturday to protest against allowing fighters back in the country.
President Beji Caid Essebsi said earlier this month that Tunisia would refuse to pardon Tunisians who fight for armed groups.
"Many of them want to return, and we can't prevent a Tunisian from returning to his country," he told AFP news agency, "but we will be vigilant."
Following a storm of criticism in the press and on social media, on December 15 he told Tunisian local television that "we will not be indulgent with the terrorists".
Source: News agencies