Ukrainian President Viktor Yanukovych on Friday signed into law strict curbs on protests condemned by the US and Europe and branded a power grab by the opposition.
The new legislation allows the authorities to jail those who blockade public buildings for up to five years. It also permits the arrest of protesters who wear masks or helmets.
US Secretary of State John Kerry called the curbs anti-democratic and wrong, while EU foreign policy chief Catherine Ashton said such actions "do not contribute to building confidence".
Western rights groups had called on Yanukovych to veto the legislation, denouncing the bills as an attempt to impose a "dictatorship."
The opposition has staged nearly two months of protests in response to Yanukovych's decision to ditch a key pact with the European Union in favour of close ties with Russia.
Ashton said before Yanukovych signed off on the legislation she was "deeply concerned by the events in Kiev", asking him to "ensure that these decisions are revised and brought in line with Ukraine's international commitments".
Ukraine's opposition fears the tough new legislation will be used to break up the opposition movement and prosecute its leaders.
The provisions, which mirror restrictive measures in place in former master Russia, are clearly aimed at the protesters in Kiev who are occupying the City Hall building and manning a tent city with massive barricades on the central Independence Square and its surrounding streets.
"This kind of anti-democratic manoeuvre is extremely disturbing and should be of concern to every nation that wants to see the people of Ukraine be able to, not only express their wish, but see it executed," Kerry said.
In a fresh sign of tension within the administration, Yanukovych's office said his chief of staff, Sergiy Lyovochkin, was standing down and would instead act as an advisor.
Lyovochkin first submitted his resignation after riot police brutally broke up an opposition protest late last year but Yanukovych refused to let him go at the time.
Yanukovych's spokeswoman Darka Chepak may also leave, a representative of the presidential administration told AFP on condition of anonymity. Chepak was not immediately available for comment.
'High security prison'
The opposition accused Yanukovych of ending democracy in the country and called on people to come out for a new monster rally on Sunday.
"Yanukovych... took a new step toward installing a real neo-dictatorship in Ukraine," the jailed opposition leader Yulia Tymoshenko said in a statement.
"The bills are a high security prison for everyone who feels like a free person," added former interior minister turned opposition leader Yuriy Lutsenko.
He invited all Ukrainians to mount a strong protest against "the ruling group of bandits", writing on his Facebook page while recovering in a hospital from an attack by truncheon-wielding police this month.
Other provisions passed Thursday introduced the term "foreign agent" to be applied to NGOs that receive even the smallest funding from foreign countries.
Russia passed a similar package of bills after Vladimir Putin was inaugurated for his third term in the Kremlin in 2012, hiking fines for unsanctioned protests, making libel a criminal offence, and slapping NGOs with the "foreign agent" label.
The German government, seen as one of the most influential voices in the European Union's dealings with ex-Soviet states, said it was watching the events in Kiev with "great concern".
"The course chosen yesterday by President Yanukovych leads to a dead end," added German Foreign Minister Frank-Walter Steinmeier.
"Repressions should not be the response to heated political discussions," Steinmeier said in a statement.
Swedish Foreign Minister Carl Bildt said on Twitter the new bills lead to a situation where "there can be no business as usual with Kiev".
"What Russia did in 60 days after Putin's (inauguration), Ukraine did in 20 minutes," the deputy chief of Human Rights Watch group Rachel Denber wrote on Twitter.
Critics voiced concern after pro-government lawmakers voted by a show of hands instead of the regular electronic system, leaving no record to verify the figure of 235 in favour out of 450 present.
[Image via Agence France-Presse]