A convoy of supporters of Ukrainian presidential candidate Viktor Yushchenko (search) was reconsidering Saturday whether to travel to the eastern stronghold of his opponent, Prime Minister Viktor Yanukovych (search), after a tense standoff with Yanukovych backers who blocked their way in a southeastern region.

Dozens of angry ethnic Russian Yanukovych supporters staged a blockade late Friday as the convoy — some 50 cars draped with Yushchenko's orange colors and carrying mostly artists and musicians touring the country to campaign for the opposition leader — sought to cross onto the Crimean peninsula, an opposition activist said.

The blockade ended peacefully overnight, and the convoy traveled on to the Crimean capital Simferopol (search), where Yushchenko's backers showed videos and photos of the massive opposition protests that swept the capital Kiev for two weeks after Yanukovych was declared the winner of the Nov. 21 runoff against Yushchenko.

Yushchenko won a Supreme Court ruling that threw out the runoff results because of fraud and ordered a repeat vote Dec. 26. The convoy, with about 150 people, is traveling around this France-sized nation of 48 million trying to sow support for Yushchenko in eastern and southern regions where Yanukovych received more votes.

Fearing possible violence in Yanukovych's hometown of Donetsk, Yushchenko's supporters were reconsidering whether to set out for the eastern city on Sunday and whether to travel without protection, convoy coordinator Olga Khodovanets (search) said.

"We might not go there without a security detail," Khodovanets said.

The leadership in the Donetsk region, the heart of the largely Russian-speaking east and south where Yanukovych draws his support, threatened to hold a referendum on autonomy as a hedge against a victory for Yushchenko, who is more popular in western and central Ukraine.

They recently canceled plans for the referendum, which had stoked fears Ukraine could split apart in the wake of the bitter presidential battle, but tension has persisted ahead of the new vote. Both sides have warned of possible provocations, and brief scuffles between supporters from opposing camps have broken out.

Yanukovych said Saturday that he could not rule out unrest after the Dec. 26 vote and that supporters might travel to Kiev to protest if they consider the balloting unfair, according to news reports. "People are just getting ready to defend their rights, their choice. They will not allow discrimination against them," he told a news conference after a rally in the southern city of Odessa, in a comment broadcast on state-run Russian television.

Outgoing President Leonid Kuchma met Saturday with a U.S. Congressional delegation led by Rep. Dana Rohrabacher, a California Republican, that arrived to push for a free and fair vote, a statement from Kuchma's office said. The visitors were also scheduled to meet parliament speaker Volodymyr Lytvyn and the head of the Central Election Commission Yaroslav Davydovych.

The decisive vote comes after revelations that Yushchenko was poisoned during the campaign.

On Friday, three separate laboratories in the Netherlands and Germany confirmed that Yushchenko was poisoned with pure TCDD, one of the most toxic chemicals. The tests also confirmed that Yushchenko's blood contained 100,000 units of the poison, the second highest concentration ever recorded.

In an interview with The Associated Press on Thursday, Yushchenko accused the authorities of poisoning him in an attempted "political murder" to push him out of the race, and said he was probably poisoned at a Sept. 5 dinner with Ukraine's security agency chief Ihor Smeshko and his first deputy Volodymyr Satsyuk.

Yuriy Pavlenko, a pro-Yushchenko lawmaker, said Saturday that opposition leaders have been "unable to establish Satsyuk's whereabouts" since Wednesday, when Lytvyn told deputies that Kuchma had fired Satsyuk.

Officials from the prosecutor general's office, which reopened its investigation into Yushchenko's illness after doctors at the Austrian clinic where he was treated said he was poisoned by dioxin, were not immediately available for comment Saturday.

Last week a parliamentary commission that earlier concluded that Yushchenko's illness was related with a viral infection also reopened its probe into the matter, and the security service also expressed its willingness to participate in the investigation.