MINSK, Belarus — Two of the Belarusian presidential candidates who were arrested in the hours after the election have been released.

Seven of the nine candidates opposing authoritarian leader Alexander Lukashenko were arrested Sunday and early Monday, some of them when riot police clashed with a crowd of thousands of demonstrators outside the main government building to protest alleged vote fraud.

The preliminary count gave Lukashenko nearly 80 percent of the vote, but international observers say the count was seriously flawed.

Candidate Grigory Kostusyev was later released and appeared at a news conference Tuesday. He said arrested candidate Dmitry Uss also had been released.

The news conference was called to announce an attempt to unify opposition forces, intimidated by the arrest of many of their leaders and hundreds of their activists.

Alexander Milinkevich, who ran against Lukashenko in the 2006 elections that were followed by several days of protests, said activists on Tuesday night will try to hold a demonstration outside the jail where many of their colleagues are believed to be held.

Kostusyev said he was held by the KGB, as the ex-Soviet republic's security service is still called, and "interrogated toughly" but that he was not physically abused.

"They wanted me to renounce and publicly condemn my colleagues ... but after I refused to do this, they let me go," he said.

The arrested include the most prominent challengers to Lukashenko, including Vladimir Neklyayev and Andrei Sannikov. Neklyayev was beaten by men in civilian clothes as he tried to lead a column of supporters into central Minsk for the protest; he was hospitalized but later taken from the hospital by unidentified men who wrapped him in a blanket. Lukashenko confirmed Monday that he was being held in a KGB prison.

In all more than 600 people were arrested; Lukashenko gave the figure as 639, but Ales Belyatsky of the Belarusian human rights organization Vesna said Tuesday that the number was around 700.