Belarusian authorities have detained another leading member of the opposition movement's coordination council.
Lawyer Maxim Znak was reportedly taken from the council's office by unidentified people in masks on Wednesday, according to his associates.
In a post on the opposition's official Telegram channel, Znak only had time to text the message "masks'' before his phone was taken away from him.
His arrest comes days after another leading member of the council, Maria Kolesnikova, was detained by Belarusian authorities.
Opposition associates of Kolesnikova say she tore up her passport at the Belarus-Ukraine border to avoid being forced out of the country.
She remains in custody on the Belarusian side of the border, although her exact whereabouts are unknown.
A third opposition figure - lawyer Ilya Salei - has also been detained, according to the Investigative Committee.
In an interview with Euronews on Tuesday Salei said Kolesnikova had been "detained by Belarusian state border committee" before confirming that her "whereabouts are still unknown."
In a statement from the state security run Investigative Committee of Belarus, Znak was detained as a "preventative measure" in an investigation for "causing harm to national security".
"Currently, investigative actions are being carried out aimed at establishing all the circumstances in the criminal case."
Meanwhile, the main opposition challenger to President Alexander Lukashenko, Sviatlana Tsikhanouskaya, left for Lithuania a day after the August 9 election, exactly one month ago.
"We keep on fighting," Tsikhanouskaya told Euronews in an interview on Tuesday, "the regime is in agony."
Unidentified people had also attempted to enter the apartment of the last member of the council's executive who remained free in Belarus - former Nobel prize laureate Svetlana Alexievich.
Leading opposition activists had formed the coordination council last month to facilitate talks with President Lukashenko for a transition of power, following last month's disputed election result.
Belarusian investigators have opened a criminal investigation into members of the coordination council, accusing them of undermining national security.
But in a statement on Wednesday, Alexievich dismissed the accusations, saying the council was seeking to defuse the crisis in Belarus.
"We weren't preparing a coup, we were trying to prevent a split in our country," Alexievich said.
Speaking to reporters from her apartment, she said she doesn't plan to leave the country despite the official pressure.
On Wednesday, the coordination council demanded "the immediate release" of Kolesnikova and Znak and also asked for "confirmation of the possible" return of Tikhanouskaya, among others who have left Belarus.
On Wednesday, Swedish foreign affairs minister Ann Linde posted an image on social media, showing Alexievich surrounded by European diplomats in Minsk.
"Harassments, arrests and forced exile of opposition in Belarus is [a] serious violation of peaceful protests," tweeted Linde.
President Lukashenko has dismissed the opposition as Western stooges and rejected demands from the European Union to engage in a dialogue with protesters.