Former Georgian President Mikheil Saakashvili has been detained in Ukraine's capital Kiev, days after his supporters freed him from a police van.
His detention, first reported on his Facebook page, was confirmed by Ukraine's Prosecutor General.
Mr Saakashvili is suspected of receiving financing from a criminal group linked to ousted Ukrainian President Viktor Yanukovych.
On Tuesday, he was dragged from his home in Kiev and arrested.
He was later freed from police custody by a crowd of his supporters. After he was freed, he urged the crowd to impeach Ukraine's President Petro Poroshenko, a former ally.
Mr Saakashvili has been leading anti-corruption rallies against Mr Poroshenko.
The authorities responded by giving him a deadline of 24 hours to hand himself in.
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, who say Mr Saakashvili is being funded by businessmen close to Russia, 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 claims the accusations are politically motivated.
He previously served as governor of the southern Odessa region after being appointed by Mr Poroshenko in 2015.
Before moving to Ukraine, Mr Saakashvili served for almost 10 years as president of Georgia.