MOSCOW — Ukraine lurched into a fresh political crisis yesterday after pro-Moscow hard-liners in the country’s parliament defied a presidential order for a dissolution and vowed to block plans to hold a snap election next month.

Amid rumors of troops being readied for a possible confrontation, supporters of Viktor Yanukovych, the Russian-speaking prime minister, pitched tents outside the parliament building in Kiev in an attempt to stop MPs being ejected by force.

The international community called for calm as MPs from Mr. Yanukovych’s ruling coalition lodged a suit in the constitutional court to overturn the decree.

Seeking to deflect charges of weakness and indecision, Viktor Yushchenko, the country’s Westernizing president, moved to end months of deadlock with his government on Monday night when he announced parliamentary elections would be held on May 27. The impasse was the latest in a series of crises since the president was swept to power during the Orange Revolution of late 2004 when hundreds of thousands gathered in central Kiev to protest against an election rigged with the suspected support of the Kremlin.

In one of the many ironies that has characterized Ukrainian politics ever since, the flags being waved in Kiev yesterday were not orange but blue-and-white, the colors associated with Mr. Yanukovych, who was initially declared winner of the suspect poll.

Branded an election cheat, his reputation was further tarnished before the poll when someone slipped dioxin into Mr. Yushchenko’s borscht, nearly killing him and leaving his face badly disfigured.

But as relentless infighting caused the Orange coalition to fall apart, the president was forced to make his archrival prime minister following a disastrous parliamentary election a year ago.

Mr. Yanukovych has sought to recast his image as a champion of democracy and peace, calling on his supporters on the streets to behave with “goodwill and love.” That has done little to quell fears of violence. Mr. Yanukovych has been accused of bussing in riot police from his strongholds in the Russian speaking east, while his supporters claim that army units loyal to the president have been issued with extra ammunition.

Both sides deny the allegations.

Lawyers were divided over whether the president had acted constitutionally in dissolving parliament. But the president insists he had no choice, saying that Mr. Yanukovych’s coalition was itself in breach of the constitution.

Since the prime minister was appointed in July, 22 MPs loyal to the president have defected to his coalition. The president says the defections are illegal. He also fears that continued defections could give the prime minister a two-thirds majority, enough to change the constitution and effectively strip him of power.