Viktor Babariko was questioned over tax evasion and money laundering allegations and denounced the action as intimidation.
Around 140 people were detained on Friday evening according to human rights group Viasna during protests across Belarus that followed the detention of a top challenger in the upcoming presidential election.
Viktor Babariko, former head of commercial bank Belgazprombank, was questioned over tax evasion and money laundering allegations and detained on Thursday.
Head of the State Control Committee Ivan Tertel said that Babariko was detained because he allegedly “attempted to pressure witnesses and conceal the trace of the previous crimes.”, citing allegations of Belgazprombank channelling over €380 million to a Latvian bank.
It follows Sunday's searches at the bank and the arrests of its 15 executives.
The episode has highlighted growing tensions between Lukashenko and Russia, the main shareholder of Belgazprombank, which has been calling for closer integration between the two countries in order for Belarus to keep receiving cheap oil and gas from Russia.
The Russian owners called the decision to introduce a temporary administration at the bank as a “flagrant violation” of Belarusian law.
Babariko denounced the authorities actions as part of an intimidation campaign.
His home was searched and his lawyers said they haven't been given access to him.
He has yet to register for the presidential race but his campaign already collected 425,000 signatures, with only 100,000 needed for his nomination.
His detention drew thousands of protesters to the streets.
The demonstrators formed a four-kilometre-long chain across downtown Minsk, waving the country's white-red-white flags used by the opposition and chanting “Freedom!”.
Belarus President Alexander Lukashenko has accused Belgazprombank's former chief executive of corruption and called him a “scoundrel.”
The 65-year-old leader is seeking a sixth term in the August 9 vote.
He's held the presidential post since the office was established in 1994.
In the run-up to the election, authorities have detained dozens of opposition activists, including popular blogger Sergei Tikhanovsk and Nikolai Statkevichi, both previously banned from running.
The crackdown on protesters has sparked concerns among EU observers, and country activists have criticised the fairness of the electoral process.