An anti-government protester holds a police shield as he stands behind burning barricades in Kiev's Independence Square February 19, 2014. [Photo/Agencies]

KIEV - Western powers threatened sanctions on Wednesday over the death of 26 people in the worst violence since Ukraine's independence from the Soviet Union, pressuring President Viktor Yanukovich to compromise with his pro-European opponents.

Yanukovich denounced the overnight bloodshed in central Kiev as an attempted coup, and his security service said it had launched a nationwide "anti-terrorist operation" after arms and ammunition dumps were looted.

US President Barack Obama said he condemned the violence in the strongest possible terms and warned of consequences if it continued, while European Union leaders said they were preparing targeted sanctions against those responsible for the "unjustified use of excessive force by the Ukrainian authorities".

EU officials said Yanukovich himself would not be on the list to keep channels of dialogue open. The foreign ministers of Germany, France and Poland will visit him on Thursday, hours before an emergency EU meeting to decide on the sanctions.

The United States urged Yanukovich to pull back riot police, call a truce and talk to the opposition.

Pentagon spokesman Colonel Steve Warren urged the Ukrainian armed forces to stay out of the conflict, warning that "participation would have consequences in our defense relationship".

Earlier on Wednesday, Ukraine's defence ministry said the armed forces might take part in a countrywide anti-terrorist operation organised by the state security service.

A presidential decree later appointed a new head of the armed forces general staff, naming navy head Admiral Yury Ilyin in place of Colonel-General Volodymyr Zamana. The decree gave no explanation for the change in personnel, nor for the timing.

Ukraine protesters end city hall occupation	EP suggests targeted sanctions against Ukraine