In near apocalyptic scenes close to parliament, several police buses and vehicles were torched by the protesters who hurled stones and Molotov cocktails at the ranks of the security forces. Police responded with tear gas and stun grenades.
The clashes further raised the stakes in the almost two month-standoff between the opposition and Yanukovych which has seen protesters seize control of the main city square in Kiev and municipal buildings.
The US embassy in Kiev urged an end to the violence, saying the Ukrainian government must "immediately start negotiations with all sides to resolve the political standoff, address protesters' concerns, and prevent violence from spreading".
Ukrainian police used tear gas, stun grenades and water cannon in a bid to disperse the hundreds of people who sought to storm police cordons near the Verkhovna Rada parliament in the capital, witnesses and AFP correspondents said. Medical workers said police had also used rubber bullets.
In some of the most violent scenes since the start of the protests, demonstrators set five buses and two trucks on fire while the air filled with the stench of tear gas and thick with the smoke from the stun grenades.
Their faces covered by scarves or ski masks, many of the protesters wielded sticks or even chains. They were confronted by helmeted riot police equipped with shields.
Health officials said 24 people were injured and three were hospitalised, while police said more than 70 officers had been hurt. Police insisted the water cannon was used to douse flames on the buses and not against protesters.
Kiev riot police said the protesters had captured a security services officer and brutally beat him up. He was then rescued but found seriously injured and in a "state of shock".
The interior ministry said four people had already been arrested and charged with mass rioting.
Klitschko meets Yanukovych at residence
Opposition leaders including former boxing champion Vitali Klitschko and Arseniy Yatsenyuk called on the protesters to refrain from using force but their calls were ignored by the more radically-minded protesters.
Amid the chaos of the clashes, Klitschko was sprayed with powder from a fire extinguisher leaving his eyes irritated and face and clothes covered in white powder.
In an apparent attempt to find a compromise, Klitschko travelled to the president's Mezhygirya residence outside Kiev to meet Yanukovych in person.
The president received Klitschko and promised early Monday to create a special commission of officials and opposition to solve the crisis, the boxer's party announced.
Klitschko had earlier called on Yakukovych to "find it in yourself not to repeat the fate of (Nicolae) Ceausescu and (Moamer) Kadhafi", referring to the slain Romanian and Libyan dictators.
He urged the president to "call early elections so that the situation does not get any worse".
Earlier, some 200,000 people had filled Kiev's Independence Square and surrounding streets for a new mass rally in defiance of new strict curbs on protests.
Yanukovych on Friday signed off on the new legislation banning nearly all forms of protest that outraged activists and troubled the West.
The new laws allow the authorities to jail those who blockade public buildings for up to five years and permit the arrest of protesters who wear masks or helmets.
Other provisions ban the dissemination of "slander" on the Internet and introduce the term "foreign agent" to be applied to non-governmental groups that receive foreign funding.
Many of the demonstrators at the largely peaceful mass rally wore cooking pots and colanders on their heads while others sported ski, medical and carnival masks to mock the new legislation.
Protesters expressed frustration at the rally over the lack of a clear programme from the opposition leaders after almost two months of protests over Yanukovych's decision to ditch a pact with the EU under Russian pressure.
The opposition leaders were whistled and heckled during the main rally for their perceived inability to mount a stronger challenge.
"Unfortunately, they have not answered a question about a main leader," protester Ruslan Koshevarov said at the rally. "There's disappointment, the politicians have not met our expectations."
Yanukovych's arch nemesis Yulia Tymoshenko remains in jail, while the protest leadership appears riven by rivalries ahead of presidential election next year.
Critics say Yanukovych has followed in the footsteps of Russian President Vladimir Putin, who pushed through similar laws after returning to the Kremlin for a third term in 2012 after huge protests.
The president on Friday dismissed his chief of staff Sergiy Lyovochkin and will skip this week's prestigious economic forum in the Swiss ski resort of Davos.