Georgia goes to the polls for crucial local elections on Saturday, amid aggravated political tensions the day after former president Mikheil Saakashvili was arrested hours after returning to the country from exile.
His arrest was announced by Prime Minister Irakli Garibashvili.
Saakashvili, 53, had said in a video posted on Facebook earlier in the day: "I risked my life and freedom to return!"
The politician, who said he was in the Georgian coastal city of Batumi, called for protests and for people to "save Georgia" at the weekend's elections.
"We all need to understand that voting for The Dream party will be the signature of the death penalty for Georgia. That's why on October 2, we should all go to the elections to save Georgia. And on October 3, from the morning of October 3, let's move from the whole of Georgia to protect the results of the elections," Saakashvili said.
Saakashvili announced earlier this week that he planned to fly to Georgia for the weekend's local elections.
But Garibashvili said on Tuesday that if Saakashvili "sets foot on Georgian soil, he will be immediately arrested and imprisoned."
The 53-year-old, who served as president from 2004 to 2013, has been accused by the Georgian judiciary of abuse of power. Saakashvili states that the case is political.
The founder of the main opposition United National Movement (UNM) party had been living in exile in Ukraine.
Georgia was plunged into a political crisis since last year when opposition parties claimed there was massive fraud in the parliamentary elections.
In May, European Council President Charles Michel brokered an exit agreement, but the Georgian Dream unilaterally pulled out after two months, drawing criticism from the EU and the US.