Mr Thaksin remains a highly divisive figure in Thailand
Ousted Thai Prime Minister Thaksin Shinawatra has been granted citizenship by Montenegro and is currently visiting the Balkan country, local police say.
They say Mr Thaksin arrived from Dubai at the weekend and there have no legal reason to arrest him.
Mr Thaksin was removed in a 2006 coup. He faces a jail sentence if he returns to Thailand, after being convicted on a conflict of interest charge.
His supporters have been holding mass street rallies in Bangkok.
They are demanding the resignation of the current government and immediate elections.
Mr Thaksin has been in self-imposed exile since 2006 - mostly in London or Dubai.
Montenegrin officials have not publicly commented on how Mr Thaksin obtained the country's citizenship.