By Richard Balmforth and Jack Stubbs
KIEV (Reuters) - Ukrainian President Viktor Yanukovich offered the opposition several top government posts on Saturday, hoping to coax his opponents into ending protests that threaten to bring the country to a standstill.
But opposition leaders, whose power base is among thousands of protesters massing in Kiev's city centre, continued to press for further concessions, including early elections and the repeal of an anti-protest law.
After meeting opposition leaders, Yanukovich offered former economy minister Arseny Yatsenyuk the post of prime minister to replace Mykola Azarov, whose government would be expected to resign, the presidential website said.
Vitaly Klitschko, a former international boxing champion, would be appointed deputy prime minister responsible for humanitarian issues, it added.
The presidency linked its offer to the opposition reining in violent protesters and quoted Yanukovich as promising that those detained during the unrest would be dealt with leniently.
It said Yatsenyuk could be given the job of heading the government of Mykola Azarov. Yatsenyuk, meanwhile, was quoted as saying the opposition was ready to "lead the country."
But Klitschko later told German newspaper Bild am Sonntag: "This was a poisoned offer by Yanukovich to divide our protest movement. We will keep on negotiating and continue to demand early elections.
"The protest by Ukrainians against the corrupt president must not have been in vain," Klitschko was quoted as saying.
The opposition has been calling for the dismissal of Mykola Azarov's government since unrest broke out two months ago after Yanukovich rejected a trade deal with the European Union in favor of closer ties with Russia.
Thousands were massed on Saturday night on Kiev's Independence Square to report on their discussions with Yanukovich.
In the past week, more radical protesters have violently clashed with police about a half mile away in front of the Dynamo Kiev football stadium.
The presidential website said Yanukovich had promised that those detained during the unrest would be dealt with leniently if the opposition reined in the radical protesters and if they persuade those who have been occupying public buildings to leave.
Ukraine's interior minister had said that all those who occupied public buildings and stayed on Independence Square - the crucible of the protest where hundreds camp overnight - would be considered by police to be "extremist groups."
Police would use force against those who went over to the side of the radical protesters, who have clashed with police in front of the football stadium since last Sunday, the minister, Vitaly Zakharchenko, said in a statement.
The overnight violence near the stadium left fires burning and smoke billowing. Protesters kept up a drumbeat of sticks on corrugated metal.
Though the violence petered out early on Saturday morning after a negotiated truce, protesters nearby stormed into the Energy Ministry.
"There was an attempt to seize the building. About 100 people came, armed. I went to them and said that if they did not peacefully leave the building, then the whole energy system of Ukraine could collapse," Energy Minister Eduard Stavytsky told Reuters by telephone.
Stavytsky, who was shown on television angrily remonstrating with a black-helmeted activist, added: "What is taking place is a direct threat to the whole Ukrainian energy system."
Hundreds of activists had already occupied City Hall and the Agricultural Ministry.
Though the protest movement - known as the "EuroMaidan" - is largely peaceful, a hard core of radicals have been fighting pitched battles with police away from the main protest on Independence Square.
The United States has warned Yanukovich that failure to ease the standoff could have "consequences" for its relationship with Ukraine. Germany, France and other Western governments have also urged him to talk to the opposition.
Russia on Saturday stepped up its warnings against international interference in Ukraine, telling European Union officials to prevent outside meddling and cautioning the United States against inflammatory statements.
"I told (U.S. Secretary of State) John Kerry that it is very important now not to interfere in the process and to avoid any statements that will only heat up the situation," said Foreign Minister Sergei Lavrov.
"I hoped he heard me," he said, in an interview with the Vesti v Subbotu state television news program.
(Additional reporting by Pavel Polityuk; Writing by Richard Balmforth and Robin Pomeroy)