The president of Ukraine has sacked his army commander and replaced him with a hardliner, hours after security forces said they would launch an "anti-terrorist" operation targeting protesters against the president's rule.

Viktor Yanukovich announced on Thursday in a brief statement that Yuri Iliin would replace Volodymyr Zamana to head the powerful post, but provided no explanation for the decision.

Al Jazeera's Andrew Simmons, reporting from Kiev, said the new army chief is considered a more hardline option - and local media suggest the president's decision was in preparation for military action against the protesters.

The announcement as the National Security Service and the Ukrainian Anti-Terrorist Centre announced action against protesters, claiming they had seized over 1,500 firearms in the last few days.

The statements follwed a night of chaos and violence in the capital, Kiev, which left a total of 26 people dead and hundreds injured. Opposition leaders urged protesters to remain on the streets to push for the removal of the president.

"Radical and extremist groups are posing a real threat to the lives of millions of Ukrainians with their actions," said national security chief Oleksandr Yakimenko said, adding that Yanukovich had been informed of the operation. The president had earlier said protesters had "crossed the limits" and ignoring democracy.

France and Germany condemned the "unspeakable, unacceptable violence" in Kiev, while the European Union's foreign policy chief, Catherine Ashton, convened an extraordinary meeting of EU foreign ministers on Thursday to discuss sanctions against the Yanukovich government.

The German chancellor, Angela Merkel, said sanctions would show Kiev that the EU was serious about the need for a return to a political dialogue.

"But sanctions alone are not enough," said Merkel, adding that it was necessary to talk to both the opposition and Yanukovich's government to help bring peace to Ukraine.

AP news agency reported that the French, German and Polish foreign ministers will meet with the Ukranian government and the opposition in Kiev.

The White House has said that the US president, Barack Obama, ahd discussed the situation in Ukraine with the French president, Francois Hollande, and was following the events closely.

Russia, Yanukovich's international ally, on Wednesday demanded that Ukrainian opposition leaders "stop the bloodshed" and said Moscow would use all its influence to bring peace to its "friendly brother state".

Ongoing clashes

Clashes with riot police started in Kiev early on Tuesday morning, after thousands of protesters marched towards parliament, where opposition leaders said the government was dragging its feet on their demand to reform the consitution and limit the president's powers.

The confrontation became deadly as police stormed barricades around the capital's Independence Square, where they were met by volleys of petrol bombs.

After shutting restricting traffic, police armed with stun grenades and water cannons moved into the square, which has been the centre of nearly three months of protests, and dismantled some of the barricades.

Yanukovich told opposition leaders that they have "crossed the limits", after the worst day of violence since the country's independence.

In a letter published on his website on Wednesday, Yanukovich accused opposition leaders of ignoring "the basic principle of democracy".

He said: "They crossed the limits when they called people to arms. And it is a blatant violation of the law. I have some advisers who try to persuade me to the use of force. But I always thought the use of force as a wrong approach."

UN Human Rights chief Navi Pillay has condemned the violence and urged all sides to show restraint. She called for an independent investigation to ensure accountability for the deadly clashes.