Ukrainian President Viktor Yushchenko has threatened to dissolve parliament following the collapse of the pro-Western ruling coalition.
In a televised address, Yushchenko said he would use his right to dissolve parliament and call early elections if a new coalition is not formed within 30 days.
He said a "political and constitutional coup" was under way in parliament after his Orange Revolution partner, Prime Minister Yulia Tymoshenko, joined ranks with the pro-Moscow opposition earlier this week.
Tymoshenko's move paved the way for the Verkhovna Rada's adoption of a series of laws weakening the president's powers, including the right to name the prime minister, and defense and foreign ministers. Yushchenko said he would veto the legislation.
"A new parliamentary coalition has been created de facto in the Verkhovna Rada," Yushchenko said. "The Yulia Tymoshenko Bloc has entered into an alliance with the Party of Regions and the Communists. And this creation is based, I stress, not on Ukraine's state interests. The democratic majority has been betrayed by [the creation of] this alliance."
In response, Yushchenko's Our Ukraine has announced that it was leaving the eight-month-old coalition it formed with the Yulia Tymoshenko Bloc, and the president warned that further action could be taken:
"From the legal point of view, I consider the events in parliament as the formal beginning of the formation of a new parliamentary coalition," he said. "If a new coalition of parliamentary factions is not formed before the deadline determined by the Ukrainian Constitution, I will use my right to dissolve the Verkhovna Rada and call early elections."
Under the constitution, parliament has 30 days to form another coalition government.
Tymoshenko, however, said Yushchenko himself had caused the collapse of the coalition.
"I regret very much that the Ukrainian president is acting in such an irresponsible way," she told a cabinet meeting. "The coalition was ruined yesterday on his own order. But I want to say once again that we believe these are simply irresponsible steps and hysteria, that the democratic coalition should continue to live and work, and I think anyone who wants to serve Ukraine understands that."
The collapse of the coalition in Ukraine has been brewing since the beginning of the year, culminating in clashes between Tymoshenko and the president over economic reforms and alleged corruption within their respective parties.
The final straw came when the Yulia Tymoshenko Bloc openly sided with opposition Party of Regions led by Viktor Yanukovych in a late-night session that began on September 1. The two groups managed to collect a previously unheard of 300 votes in the 450-seat parliament in four separate votes, more than the majority needed to override presidential vetoes.
Serhiy Taran from the International Democracy Institute, a think tank based in Kyiv, says that upcoming presidential elections are the main reason behind the crisis.
"We cannot say that there is some attempt to grasp power," he says. "We cannot say that some parties or politicians do something illegal. We cannot say that there is some attempt to break integrity of Ukraine. We can only say that because of the disagreement for the candidacy for presidential elections the democratic coalition came to the end."
Taran says the crisis effectively marks the beginning of the campaign for the elections to be held in 2009 or 2010, with both jockeying for position. He says it is unlikely that early parliamentary elections will be held.
RFE/RL correspondent Valentinas Mite contributed to this story; with agency reports