Updated 12:26 p.m. ET

DAVOS, Switzerland —The World Economic Forum in Davos has withdrawn an invitation to the Ukrainian prime minister to address a session on Friday afternoon or attend the forum entirely, two sources said, amid spiraling violence in Kiev that has killed at least three protesters, two of them shot dead.

The move against Prime Minister Mykola Azarov points to the growing isolation of the government of President Viktor Yanukovych, which has refused to take responsibility for the deaths of anti-government protesters, at least two of whom were shot dead by snipers. Azarov — who one source said is "already in town" — earlier blamed the deaths on the opposition.

A spokesman for the forum at Davos declined to comment.

Another representative of the Yanukovych government, Deputy Prime Minister Yuriy Boyko, has come under siege from concerned Western officials at Davos. An off-the-record session framed as a discussion of Ukraine's economic future turned into an emotional dissection of Ukraine's political crisis beginning with a moment of silence for the slain protesters.

Ukrainian opposition leader Vitaly Klitchko canceled his visit to Davos and was in Kiev holding talks with Yanukovych in hopes of ending the violence. Instead, Petro Poroshenko, a billionaire, longtime politician, and former foreign minister, took the lead and urged the U.S. to freeze the assets of and launch money-laundering investigations into members of the Ukrainian government in response to the deaths.

The U.S. embassy in Kiev on Wednesday announced it had "revoked the visas of several Ukrainians who were linked to the violence." Poroshenko urged the U.S. to go further. "This morning, at 8 a.m., 100 meters from me, a peaceful protester was shot dead," Poroshenko told BuzzFeed at Davos, to where he had flown earlier Wednesday.

He called on the U.S. and EU to coordinate sanctions against Ukraine's government, and said the fact that protesters had been peacefully demonstrating since November proved they did not provoke the violence that hit Kiev this week.

Catherine Ashton, the EU's foreign policy chief, issued a statement condemning the violence: "I call on everyone involved to ensure restraint. The use of force and resort to violence is not an answer to the political crisis." While she refrained from calling out the Ukrainian government, privately, EU officials are understood to have taken a tougher tone with the Ukrainian leadership.

Estonian President Toomas Hendrik Ilves, who was involved in talks last year aimed at urging Ukraine to sign an agreement pledging closer ties to the EU, said the statement "was a first reaction to the killings, but once the EU comes together and discusses the situation, I have a suspicion that the reaction will be tougher."

Yanukovych's decision to abandon the EU agreement in favor of closer ties to Russia is what first brought protesters to the streets of Kiev in November.