The three previous post-Soviet presidents of Ukraine have all given their support to protesters who are angry at the government's decision not to sign an association deal with the European Union.
Leonid Kravchuk, Leonid Kuchma and Viktor Yushchenko have expressed "solidarity" with peaceful demonstrations, according to Mr Yushchenko's party website.
"We express solidarity with the peaceful civic actions of hundreds of thousands of young Ukrainians," the three former presidents say in a statement reported by the BBC.
Condemning "the excessive use of force against peaceful demonstrators" they have urged protest leaders and the government to engage in open dialogue, taking into account the "European aspirations of the Ukrainian people".
Tens of thousands of people have surrounded government buildings in Kiev.
There is concern for nine people beaten by police at the major demonstration in Kiev on 1 December. Relatives say six are in intensive care while three others are in prison medical units, and have been denied legal assistance.
Thirty-five people arrested as they attended the same protest have been detained for two months while awaiting trial.
Friends of those held say they were ordinary citizens rather than activists or protest organisers.
Lavrov warns Nato
Meanwhile Russian foreign minister Sergei Lavrov has warned Nato against interfering in Ukraine.
"I hope that Ukrainian politicians will be able to resolve the situation peacefully," he said at a meeting with Nato foreign ministers in Brussels.
Nato had earlier condemned the use of "excessive force" against the protesters.
The protests - the largest since the pro-democracy Orange Revolution in 2004 - flared when, under pressure from Russiam President Viktor Yanukovych abruptly froze plans to sign an EU trade and reform deal.