Kiev, Ukraine ? 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 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 today 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.