Ms. Tikhanovskaya, a former English teacher, emerged as the face of the campaign against Mr. Lukashenko in recent weeks, with the established opposition figures, including her husband, in jail or in exile. The Belarus authorities allowed her name on the presidential election ballot, and the campaigns of two other challengers to Mr. Lukashenko — Viktor D. Babariko, a jailed ex-banker, and Valery V. Tsepkalo, who fled the country — endorsed her.
She traveled the country holding campaign rallies, exhorting Belarusians tired of years of economic stagnation and political repression under Mr. Lukashenko to call for change. The official results gave her just 10 percent of the vote in Sunday’s election, compared with 80 percent for Mr. Lukashenko, but the results were denounced as fraudulent by both the opposition and international governments.
On Monday, Ms. Tikhanovskaya visited the Central Election Commission headquarters in Minsk to officially contest the vote count. She was left in a room for three hours with two senior security service officials, according to Maria Kolesnikova, a supporter of Ms. Tikhanovskaya who said she accompanied her and waited outside the room during that meeting.
About an hour into the meeting, Ms. Kolesnikova said she saw several people with black bags containing what looked like video equipment enter the room. After another two hours, Ms. Kolesnikova was told that Ms. Tikhanovskaya had departed through another entrance.
She said she has not heard from Ms. Tikhanovskaya since, but added that it was clear that the candidate had recorded her video and left the country under pressure, with her husband, her friends and her supporters in custody.
“When all those around you and your family are hostages, it is very difficult not to make statements under pressure,” Ms. Kolesnikova told reporters in Minsk on Tuesday.
Mr. Linkevicius, the Lithuanian foreign minister, said in a news conference that Ms. Tikhanovskaya was in his country, where she had been together with her children.