EU leaders will hold emergency video talks on Wednesday on the crisis in Belarus, where protests are swelling against the disputed re-election of President Alexander Lukashenko.
The meeting was called by EU Council President Charles Michel after Russia said it was ready to provide military help to its ally Lukashenko, who has ruled Belarus for 26 years.
Tens of thousands of people have taken to the streets to condemn Lukashenko's election win and a subsequent violent crackdown on protesters by riot police.
"The people of Belarus have the right to decide on their future and freely elect their leader," Michel tweeted, saying Wednesday's virtual meeting would begin at 12:00 pm (1000 GMT).
"Violence against protesters is unacceptable and cannot be allowed."
A European source said Michel decided to call the summit in view of the spike in tensions over the weekend.
Ursula von der Leyen, the European Commission president, welcomed the talks, tweeting: "The people of Belarus need to know that the EU stands by them firmly, and that those responsible for human rights violations and for violence will be sanctioned."
Lukashenko claimed victory in the August 9 election with 80 percent of the vote, despite wide opposition to his rule.
The crackdown by security forces has seen more than 6,700 people arrested, hundreds wounded and two people killed.
EU foreign ministers on Friday agreed to draw up a list of targets in Belarus for a new round of sanctions in response to the crackdown and on Monday Germany, which currently holds the EU's rotating presidency, said it was ready to back even tougher measures.
Describing a huge protest in Minsk on Sunday as "the largest rally in Belarusian modern history", the EU's foreign policy chief Josep Borrell demanded a "thorough and transparent investigation" into alleged abuse against those detained by police.
"The sheer numbers clearly show that the Belarusian population wants change, and wants it now. The EU stands by them," Borrell said in a statement issued on Monday.