Ukrainian opposition leaders are due to meet President Viktor Yanukovych, a day after the first deaths in protests that have gripped Kiev for two months.
A fragile truce is being observed but opposition leader Vitali Klitschko said he would lead pro-EU protesters "on the attack" if elections were not called.
Mr Yanukovych has asked the speaker of parliament to hold an emergency session next week to discuss the crisis.
Two activists were killed in clashes with police in Kiev on Wednesday.
Prosecutors confirmed they had died from gunshot wounds. They were the first fatalities since the anti-government protests flared up in late November over Mr Yanukovych's decision to pull out of a landmark treaty with the EU.
A third activist, Yuriy Verbytsky, has been found dead in a forest outside Kiev, after reportedly being abducted along with fellow activist Ihor Lutsenko earlier this week. His body is said to bear signs of torture.
The centre of the capital remains extremely tense, the BBC's Daniel Sandford reports.
Ukrainian media now say that protesters have taken over the regional state administration buildings in the western cities of Lviv and Rivne, and that the governor of the Lviv region, Oleg Salo, has been forced to resign.
Other unconfirmed reports spoke of attacks on the governor's offices in Zhytomyr, Khmelnytskiy and Ivano-Frankivsk.
Dead men named
President Yanukovych has assured the head of the European Commission, Jose Manuel Barroso, he will not introduce a state of emergency. The two had spoken by phone, the Commission said on Thursday.
But Mr Yanukovych said he had asked the speaker of Ukraine's parliament to hold an emergency session next week.
The speaker said the session would discuss opposition calls for the government to step down and recently-passed anti-protest laws.
Before heading to his talks with Mr Yanukovych, Mr Klitschko urged both the protesters and police to refrain from any further use of force until he reported back on Thursday evening.
He is bringing three main demands to the talks: a snap presidential election, the cancellation of the new anti-protest laws and the resignation of the government.
Addressing protesters on Wednesday, he said the president could end the stand-off "without bloodshed". Otherwise, he added, "we will go on the attack".
Prime Minister Mykola Azarov said opposition leaders should be "more humble" and "move away from the language of ultimatums".
Russian news agencies quoted him as saying that "a genuine attempt at a coup d'etat is being carried out".
Hundreds of protesters and scores of police officers have been injured in clashes around Kiev's Independence Square this week.
Officials confirmed two bodies were found with bullet wounds close to the scene of clashes on Wednesday.
One of those killed was identified as Serhiy Nihoyan, the 20-year-old son of Armenian refugees from Nagorno-Karabakh, who travelled from his home in eastern Ukraine in December to join the protests.
The other man shot was named as Belarusian citizen Mikhail Zhyznewski, who was at the protest with Una-Unso, a Ukrainian far-right group.
Another man was also reported to have died after falling from the top of the Dynamo football stadium. However, a spokeswoman for Kiev's health department said he had survived the fall.
Mr Azarov denied that police were responsible for the deaths, saying they were not carrying live ammunition.
The BBC's Duncan Crawford spoke to a student, Mikhail Nizkoguz, 17, who accused riot police of dragging him from the street on Monday and torturing him by beating and stabbing.
His face and body is covered with cuts and bruises. He said police accused him of firing fireworks at them - but that he was only taking pictures.
A police press spokesperson in Kiev told the BBC they know nothing about any cases of alleged torture.
According to a list on the website of Ukrainian media non-governmental organisation Imi, 42 journalists were also hurt this week alone.
The European Union said earlier it would "rethink" its relationship with Ukraine if there was a "systematic violation of human rights".
The US accused the Ukrainian government of failing to "engage in real dialogue" and revoked the visas of "several Ukrainians who were linked to the violence". It did not give names.
Russia has accused the EU and US of "outside interference" in Ukrainian affairs.
"The extremist part of the opposition is crudely violating the country's constitution," said Russian Deputy Foreign Minister Grigory Karasin.