Former Georgian President Mikheil Saakashvili has been detained in Ukraine's capital Kiev, days after his supporters freed him from a police van.
Mr Saakashvili, who in 2015-16 served as regional governor in Ukraine under President Petro Poroshenko, has been leading anti-corruption rallies against his former ally.
On Tuesday, he was dragged from his home in Kiev and arrested.
He has been calling for Mr Poroshenko's impeachment since his first arrest.
The authorities responded by giving him a deadline of 24 hours to hand himself in.
Mr Saakashvili is accused of receiving financing from a criminal group linked to ousted Ukrainian President Viktor Yanukovych.
His detention was part of an operation "to disrupt a plan of revenge of pro-Kremlin forces in Ukraine", Ukraine's Prosecutor General Yuriy Lutsenko said on Tuesday.
Prosecutors released audio and video recordings which they say proved he had received hundreds of thousands of dollars from the criminal group.
Mr Saakashvili said the recordings were fake.
If found guilty, he could face up to five years in jail.
Mr Saakashvili also faces the threat of extradition to Georgia, where he is wanted on corruption charges. He says the accusations are politically motivated.
He was governor of the southern Odessa region for 18 months after being appointed by Mr Poroshenko in 2015.
Before moving to Ukraine, Mr Saakashvili served for almost 10 years as president of Georgia.