MOSCOW -- Russia increased pressure on U.S. Congress on Friday not to pass legislation that would punish Russian officials for human rights violations, warning Washington that it had prepared tough retaliatory measures.

Congress was due to vote on a bill named after Russian lawyer Sergei Magnitsky later Friday, the third anniversary of his death in detention. The bill is designed to deny visas for officials involved in his imprisonment, abuse or death.

Deputy Foreign Minister Sergei Ryabkov said Russia had already prepared its response but gave no details other than a Foreign Ministry statement on Thursday warning of tough retaliation against "unfriendly and provocative" legislation.

"Of course there are (measures in place). We have discussed (them) at all stages of the debate over the so-called Magnitsky bill," Interfax news agency quoted Ryabkov as saying. "I can confirm that our response will be tough."

Possible sanctions against US officials
He gave no details but Russian officials have indicated that Moscow would retaliate by imposing sanctions on U.S. officials it accused of violating Russian citizens' rights.

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They would be likely to include officials involved in refusing a Russian request for the extradition of a convicted arms trader, Viktor Bout, serving a 25-year prison term in the United States.

The rhetoric became more heated this week as the vote neared. Adoption of the bill -- and any reprisal -- could damage efforts to improve relations between the former Cold War enemies at the start of President Barack Obama's new term, and a few months after Vladimir Putin's return to the Kremlin.

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During his first term in office, Obama initiated a "reset" in relations after bilateral ties sank to a low after a 2008 war between Russia and pro-Western Georgia. But recent months have seen both successes and strains in U.S.-Russian relations.

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The House of Representatives voted Thursday to include the legislation in a broader package to extend "permanent normal trade relations," or PNTR, to Russia following its entry to the World Trade Organization in August.

'Horrendous and unacceptable'
Magnitsky was jailed in 2008 on suspicion of tax evasion and fraud, charges which colleagues say were fabricated by police investigators he had accused of stealing $230 million from the state through fraudulent tax refunds.

The Magnitsky case has become a symbol of corruption and the abuse of citizens who challenge the authorities in Russia, where the Kremlin's own human rights council has said he was probably beaten to death.

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Rep. David Dreier, the Republican chairman of the House Rules Committee, said on Thursday that such action in a country "that claims to be a democracy ... is horrendous and it is unacceptable."

Congress must approve PNTR to ensure that American companies receive all the market-opening benefits of Russia's entry into the World Trade Organization in August.

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U.S. business backs the combined trade and human rights bill out of a belief that the benefits from approval of PNTR will outweigh negative fallout from the Magnitsky portion of the legislation.

Russia's entry into the WTO after 18 years of negotiations and strong support from Obama obliges the United States to lift a Soviet-era amendment that linked favorable U.S. tariffs on Russian goods to the rights of Soviet Jews.

The amendment is outdated, but U.S. lawmakers are reluctant to remove it without passing legislation to keep pressure on Moscow over their human rights concerns, which have deepened since Putin returned to the presidency in May.

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If the House approves the bill, it will then go the Senate, where supporters are optimistic it will be approved. Obama is expected to sign the bill, even though the White House preferred legislation without the human rights sanctions provisions.

The two countries negotiated a simplified visa process earlier this year. But Moscow's closure of a U.S. international aid agency office and accusations that Washington was meddling in Russian politics undermined prospects for better relations.

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