"We announce an opposition to the current government," a statement said. "We call on the ministers from the Our Ukraine block to tender their resignations."
The bloc, which won 80 seats in the 450-member Supreme Rada during the March 26 elections, was part of the first parliamentary coalition to emerge after the elections, along with the Yulia Tymoshenko Bloc, which won 129 seats, and the Socialists (33 seats).
But the alliance collapsed when the Socialists defected to join the Party of Regions, led by President Viktor Yushchenko's former rival in the 2004 election, Viktor Yanukovych. And Our Ukraine was in talks with the ruling coalition of the Party of Regions, the Socialists and Communists over forming a broad coalition of national unity.
The two-month talks ended in a statement by Roman Bezsmertniy, head of Our Ukraine's parliamentary faction, over plans to join the opposition.
The Our Ukraine bloc accused Prime Minister Yanukovych last month of breaching agreements set out by the national unity pact on Ukraine's NATO membership drive.
An opposition bloc was officially proclaimed late September by Yulia Tymoshenko, the darling of the 2004 "orange revolution" that brought Yushchenko to power and the previous premier-in-waiting in the first post-election coalition, whose eponymous bloc managed to sign a pact with two Socialist Party deputies.
