KIEV, Ukraine (AP) – Supporters of Ukrainian presidential candidate Viktor Yushchenko reconsidered plans to travel to his opponent’s eastern stronghold after a tense standoff, and a U.S. congressional delegation arrived in Ukraine Saturday to press for fairness in the Dec. 26 runoff election.

Meanwhile, a top security agency official whose house was pinpointed by Yushchenko as the probable site of his poisoning denied any involvement in slipping the opposition leader a dose of the toxic chemical dioxin.

Dozens of angry ethnic Russian supporters of Prime Minister Viktor Yanukovych 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, said convoy coordinator Olga Khodovanets.

Yushchenko’s backers then traveled on to the Crimean capital Simferopol, where they showed videos and photos of the massive opposition protests that swept the capital Kiev for two weeks after Yanukovych, Ukraine’s Prime Minister, was declared the winner of the first runoff vote on Nov. 21.

Yushchenko won a Supreme Court ruling that threw out results of that election 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 or Monday and whether to travel there without protection, Khodovanets 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 eastern Ukraine, threatened to hold a referendum on autonomy as a hedge against a victory for Yushchenko, who is more popular in the Ukrainian-speaking west.

The regional leaders 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,” Yanukovych said at a news conference.

“They will not allow discrimination against them,” he added at the news conference after a rally in the southern city of Odessa, in a comment broadcast on state-run Russian television.

The United States had refused to recognize the result of the Nov. 21 runoff, and a U.S. delegation led by Rep. Dana Rohrabacher, a California Republican, met with outgoing President Leonid Kuchma to call for a free and fair rerun.

“We will cross our fingers for Ukraine,” Rohrabacher said after the meeting.

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.

Yushchenko accused the authorities of poisoning him in an attempted “political murder” to push him out of the race, saying in an interview with The Associated Press that he was most likely poisoned at a Sept. 5 dinner with Ukraine’s security agency chief Ihor Smeshko and his first deputy, Volodymyr Satsyuk.

In an interview with the Stolichnye Novosti newspaper published Saturday, Satsyuk denied he had “any involvement in Yushchenko’s poisoning.”

Satsyuk said there were four people at the dinner at his dacha – himself, Yushchenko, Smeshko and David Zhvanya, a lawmaker and Yushchenko ally. He said that Zhvanya organized the meeting, and that it had been postponed from Sept. 4 because Yushchenko and Zhvanya were busy.

“All food products were on the table on common plates. The food was served by the two people and cooked by another one in the kitchen,” Satsyuk told Stolichnye Novosti.

He said he was ready to meet Yushchenko in public.

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

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.

Ukraine’s election strained relations between Russia and the West, with each accusing the other of interference, but Russian Foreign Minister Sergey Lavrov expressed confidence Saturday that the issue would not create a new divide.

“If somebody gets into his head the idea of building a new wall between Ukraine’s eastern border and (Russia), I think that would just be such clearly recidivist Cold War thinking that most European countries, and the United States too, would rebel against it,” Lavrov said on Moscow’s TV-Tsentr.