But the protests are spearheaded by former Georgian president Mikheil Saakashvili, a man of preternatural energy and self-assurance who has already overthrown one regime.
General Prosecutor Yuriy Lutsenko, who says Saakashvili is suspected of assisting a criminal organization, said the opposition leader had been detained by police in Kyiv and was in a temporary detention facility.
The situation near parliament was calm at around 1230 GMT, although an increased number of armoured police stood guard around the building, according to a Reuters witness.
The head of the International Monetary Fund, Christine Lagarde, said she had a constructive phone call with Ukrainian President Petro Poroshenko late on Thursday in which she urged him to speed up the fight against corruption.
Saakashvili dramatically escaped from a security service van on Tuesday after it was swarmed by hundreds of supporters angered at his detention.
Saakashvili became a regional governor in Ukraine in 2015 at Poroshenko's invitation but they later fell out.
Saakashvili later said police had searched the wrong tent at the camp, continuing a surreal hide-and-seek game between him and Ukrainian law enforcement ever since he barged across the border from Poland three months ago. The saga threatens to embarrass the pro-Western authorities at a time when they face a chorus of criticism from reformers and foreign donors over perceived backtracking on reforms and attacks on anti-corruption institutions. "If he flees from the investigation, this undermines his credibility", he said.
Saakashvili said he will not turn himself in, though prosecutors were welcome to see him at the camp outside the Supreme Rada where about 100 supporters gathered.
Mr Saakashvili has been leading anti-corruption rallies against Mr Poroshenko. A dozen members of the anti-corruption committee on December 6 voted to recommend that the parliament dismiss Sobolev from his post as they were unsatisfied with his work in the committee.