Hundreds of protesters have clashed with riot police in the Ukrainian capital, Kyiv.
The clashes on January 19 came after tens of thousands of protesters gathered in Independence Square in defiance of new antiprotest legislation.
Protesters attacked police with sticks as they tried to push their way toward the parliament building, which had been cordoned off by rows of police and buses. S
Stun grenades were used and smoke was seen above the crowd.
Before the clashes erupted, opposition leader Vitali Klitschko called the new antiprotest laws illegal and "unconstitutional."
The new legislation was rushed through parliament on January 16 and signed by Yanukovych the next day.
The United States and European Union have called the new measures anti-democratic. Ukraine's opposition accuses Yanukovych of trying to install a "dictatorship."
WATCH: Live footage of the unrest in Kyiv (natural sound):
Tensions remain high in Ukraine since Yanukovych's abrupt decision late in November not to sign a deal with the EU, sparking some of the biggest protests in the country since the 2004 Orange Revolution. Yanukovych allegedly changed course after pressure from the Kremlin, which has since offered financial aid and cheaper gas to cash-strapped Ukraine.
The new laws ban any unauthorized installation of tents, stages or amplifiers - all features of the protests that play out day and night on Kyiv's Independence Square.
The laws allow prison terms of up to 15 years for "mass violation" of public order.
The new legislation also requires non-governmental organizations to register as "foreign agents" if they are funded from abroad, mirroring a similar rule on the books in Russia.
Analysts say the protests do not appear to have shaken Yanukovych's hold on power. But Yanukovych's decision late on January 17 to sack his chief-of-staff, analysts say, indicates that tensions are simmering within the Ukrainian leader's inner circle.
The president's office gave no reason for the dismissal of Serhiy Lyovochkin.
Lyovochkin was reported to have considered stepping step down back in November after riot police brutally dispersed student protesters.
The AFP news agency quotes an unnamed Ukrainian official as saying Yanukovych's spokeswoman, Darka Chepak, is also considering stepping down.
"Turmoil in regime in Kyiv. Reports of resignations, dismissals and general uncertainty," Swedish Foreign Minister Carl Bildt wrote on Twitter.
With reporting by AFP and Reuters