Some 200,000 Ukrainian protesters massed in central Kiev on Sunday in defiance of hugely controversial new curbs pushed through by President Viktor Yanukovych in a bid to suppress a pro-EU protest movement.
Many demonstrators wore pots and colanders on their heads while others sported ski, medical and carnival masks to mock the new legislation which forbids protesters from covering their faces.
Waving blue and yellow national flags and the red and black banners of the war-time Ukrainian Insurgent Army and chanting "Glory to Ukraine," protesters filled Kiev's central Independence Square and surrounding streets to bursting point.
"We declare the legislation adopted on Thursday illegal," Vitali Klitschko, former world boxing champion and one of the opposition leaders, told the crowds. "Yanukovych and his stooges want to steal our country."
Yanukovych, 63, who has been wrestling with two months of opposition protests, on Friday signed into law tough legislation that bans virtually all forms of protests in a move the opposition called a power grab and the West said was anti-democratic.
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.
"Parliament has lost its legitimacy, which means we should create a people's council consisting of opposition politicians," opposition leader Arseniy Yatsenyuk told the rally.
The protest curbs are expected to breathe new life into the demos against Yanukovych, whose decision to ditch a key pact with the EU in November in favour of closer ties with Moscow sparked the largest rallies since Ukraine's 2004 pro-democracy Orange Revolution.
At the height of the protests last month, tens of thousands took to the streets calling for the president's resignation and early polls.
But the opposition has so far been unable to unseat Yanukovych, who faces election early next year, and on Sunday the three main opposition leaders including Klitschko and Yatsenyuk were jeered by the crowds.
"We cannot wait any longer. We have no choice: either we win or we will slide into dictatorship," said one protester, Sergiy Nelipovych, speaking at the protest camp on Independence Square ahead of the rally.
The opposition fears that the government will use the new legislation to prosecute its leaders and break up the protest movement.
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 against his decade-long rule.
US Secretary of State John Kerry called Thursday's snap vote in the Ukrainian parliament anti-democratic and wrong, while EU foreign policy chief Catherine Ashton said such actions "do not contribute to building confidence".
In a sign of mounting tensions, the president on Friday dismissed his chief of staff and will skip this week's prestigious economic forum in the Swiss ski resort of Davos.
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.
Jailed opposition leader Yulia Tymoshenko has accused her arch-rival Yanukovych of seeking to establish a "neo-dictatorship".
The protests in Ukraine have over the past few weeks repeatedly descended into clashes with police in which hundreds of people have been hurt.