* Bubka says "shocked" by deaths
* IOC boss says Ukraine athletes competing with dignity
* At least 26 protesters, police killed (Updates with IOC President reaction, fresh Bubka comments)
By Karolos Grohmann
SOCHI, Russia, Feb 19 (Reuters) - Ukrainian Olympic Committee chief Sergey Bubka on Wednesday called for an end to violence that has gripped his country as Ukraine's athletes struggled to focus on competing at the Sochi Winter Games.
International Olympic Committee (IOC) President Thomas Bach praised Ukraine's athletes for competing with "great dignity" despite the violence back home.
Former pole vault champion Bubka, an IOC Executive Board member, was shocked by the events unfolding in Ukraine.
"I couldn't believe, I cannot believe it's happened, and we are in such a difficult situation today," said Bubka, who is also an adviser to the president of Ukraine.
At least 26 people were killed in anti-government protests, and on Wednesday President Viktor Yanukovich accused pro-European opposition leaders of trying to seize power by force as demonstrators again took to the streets.
"I pray, and again I appeal to both parties to stop violence," Bubka told international news agencies.
"Try to find the peace. Try to find, keep us together and live in peace, because this is most important. For us, what happened in Ukraine is a big shock."
Bubka, a leading sports figure in his country, said he had requested athletes competing in Sochi be allowed to wear black armbands but the IOC turned it down.
"This is not possible. The IOC during Sochi had already some other requests, and they said 'we understand, ... your athletes can go to (press) conferences. They can express their sadness, express condolences,' but we should respect Olympic charter," said Bubka.
IOC President Bach extended condolences to the victims' families and praised Ukrainian athletes for continuing to compete in Sochi.
"I would like to offer my condolences to those who have lost loved ones in these tragic events," Bach said. "Our thoughts and sympathy are with the Ukrainian team at what must be a very difficult time.
"The way they have continued to represent their nation with great dignity is a credit to them and their country. Their presence here is a symbol that sport can build bridges and help to bring people from different backgrounds together in peace."
The unrest has spread to at least three cities in the western part of the country.
Police said protesters had seized regional administration headquarters in the cities of Ivano-Frankivsk and Lviv, which is bidding for the 2022 Winter Olympics with Bubka as one of the bid leaders.
Media said protesters torched the main police station in the city of Ternopil.
"I think they should stop it for the Olympics ... Now in Ukraine they're going mad," said Dmytro Mytsak, a Ukrainian giant slalom skier from Kiev competing in Sochi.
The 18-year-old said his parents had not mentioned the violence when they spoke before his race on Wednesday, but he was already aware of the deaths.
"We're trying not to talk about this and not to think about it for the time being. Of course it's sad what's happened," he told Reuters.
"Yes it's a distraction, everyone's talking about it - even just now at the start, at the finish, people are saying, 'what's happened in your country, what's happened?'
"We're getting support from the Russian spectators and I'm grateful for that."
Many people have been killed by gunshot and hundreds have been injured, with dozens in a serious condition, police and opposition representatives said.
"Those are terrible scenes," IOC spokesman Mark Adams told reporters. "I'm sure that the Olympic truce is an important, symbolic thing for us - I'm not sure really that it plays much part in what's gong on there.
He added that any talk of the Lviv bid, for which Bubka is a leading figure, was secondary at the moment.
"In terms of Lviv and the bid, I think at this stage with the terrible things that are going on at the moment, I think we should concentrate on what's going on there and hope that solves itself in as peaceful a way as possible."
"It is not really right to be speculating on an Olympic bid when such things are happening."
Lviv is up against Poland's Krakow, Beijing, Kazakhstan's Almaty and Norwegian capital Oslo with a shortlist of cities to be drawn up in five months. (Additional reporting by Mark Trevelyan in Rosa Khutor and Catherine Koppel in Sochi. Editing by Mike Collett-White/Peter Rutherford)