Several thousand protesters remained on Kyiv's Independence Square on Thursday morning after spending another night in subzero temperatures.

Following an unsuccessful attempt by riot police to clear the square early on Wednesday, some protesters filled sandbags with snow and piled them up to reinforce barricades that had been partially dismantled by the security forces. No violence was reported overnight.

The United States responded to the news of those clashes, in which about 30 people were injured, by issuing its strongest warning so far against use of force against peaceful protesters, saying it was considering imposing sanctions President Viktor Yanukovych's government.

"We are considering policy options. There obviously has not been a decision made. Sanctions are included but I am not going to outline specifics," US State Department spokeswoman Jen Psaki told reporters in Washington.

"It's important to convey our support for their ability to voice their views, support for their efforts on European integration, our belief that respect for democratic principles, including freedom of assembly, is a universal right," she added.

Earlier in the day, US Defense Secretary Chuck Hagel used a telephone conversation with his Ukrainian counterpart, Pavlo Lebedev, to warn against using military force against the demonstrators.

A statement issued by Pentagon spokesman Carl Woog said Hagel had "underlined the potential damage of any involvement by the military in breaking up the demonstrations."

It also said that Lebedev had reassured Hagel that President Yanukovych had no intention of using the army against the protesters.

The European Union's foreign policy coordinator, Catherine Ashton, meanwhile, held two rounds of talks with Yanukovych in Kyiv this week, in which she sought to bring the two sides together for a negotiated resolution.

Opposition pledge bigger protests

The opposition meanwhile, has said its intends to bring even more people out onto the streets. Local media reported that dozens of buses and private vehicles had arrived in the capital from all over the country early on Thursday.

Opposition leader Vitali Klitschko said in an article published in the Thursday edition of Germany's mass-circulation Bild newspaper, that he expected "millions of people on the streets, more than ever before" in the next few days.

In light of the use of force against the demonstrators, Klitscho also rejected President Yanukovych's offer of talks.

The protests against Yanukovych gathered steam almost a fortnight ago, when he balked at signing an agreement that would have increased political and business ties with the EU, in favor of maintaining and possibly intensifying close relations with Russia.

pfd/kms (Reuters, AFP, dpa)