Thousands of protesters attacked the ruling-party headquarters and tried to march on parliament, reports said.
Tumultuous scenes have also been reported inside parliament
where opposition MPs are pushing for a vote on replacing the
constitution.
The move is aimed at curbing President Viktor Yanukovych’s powers.
The opposition has repeatedly warned that failure to act will further inflame mass anti-government protests.
Ukraine’s unrest began in November, when Mr Yanukovych backed
away from an association and free trade deal with the European Union,
and instead agreed to a loan from Russia.
Moscow wants Ukraine to join the Russia-led customs union, where Belarus and Kazakhstan are also members.
Both the EU and Russia have accused each other of interfering in Ukraine’s affairs.
Tens of thousands of protesters trying to march on the
parliament building have been blocked by lines of police vehicles,
according to reports from Kiev.
Some are ripping up cobblestones to throw at police, and
others are throwing smoke bombs, while police are responding with stun
and smoke grenades and rubber bullets.
Protesters also attacked the headquarters of President Yanukovych’s ruling party.
Several people have been injured, both protesters and police officers, local media reported.
Inside parliament, reported Interfax-Ukraine news agency,
about 50 opposition MPs blocked the parliamentary rostrum in protest
after parliamentary staff refused to register their resolution on
reinstating the 2004 constitution.
“Our deputies have just returned from the draft law
registration section. They have just simply locked the doors there on
the instructions of [Speaker Volodymyr] Rybak and are refusing even to
talk to Ukrainian people’s deputies, let alone register the resolution,”
opposition leader Arseniy Yatsenyuk was quoted as saying.
The opposition has been pushing for weeks for a return to the
2004 constitution, which would mean President Yanukovych losing some of
the powers he has gained since his election in 2010.
The changes would mean that parliament – not the president –
would appoint the prime minister and most cabinet members, as well as
regional governors.
The move could also lead to snap presidential elections – a key demand of the opposition.
MPs who support the president have argued that different
proposals on how to return to the previous constitution legitimately
have not been thoroughly discussed, and more time is needed to iron out
all the differences between the two sides.
In a separate development, Russian Finance Minister Anton
Siluanov said Moscow would provide Ukraine with a new $2bn (£1.2bn)
tranche of aid “this week”.
In December, Moscow pledged $15bn to back Ukraine’s struggling economy, but so far only $3bn has been transferred.
The Kremlin had hinted it would freeze the aid until a new
government acceptable to Moscow was formed after Ukrainian PM Mykola
Azarov resigned last month.
On Monday, an amnesty for anti-government protesters in
Ukraine came into force after demonstrators ended their occupation of
government buildings in Kiev and in the regions.
Protesters had held some of the buildings for more than two months.
But a sprawling tent city remains in Kiev’s central square, where some denounced the decision to end the occupations.
