MOSCOW -- U.S.-Russia ties have again plunged into acrimony amid disputes ranging from disagreement on Syria to Russian President Vladimir Putin's clampdown on dissent.

A U.S. bill intended to lift Cold War-era trade restrictions but also containing sanctions against Russian officials accused of rights abuses has become the latest flash point, with Moscow venting its outrage and threatening a quid pro quo.

While U.S.-Russia ties haven't yet reached the lows seen during George W. Bush's presidency, a senior Russian lawmaker warned Friday that the legislation approved by the Senate could be a prologue to an even deeper crisis.

Alexei Pushkov, the Kremlin-connected head of the Foreign Affairs committee in the lower house of Russia's parliament, said that Moscow was particularly annoyed by U.S. Secretary of State Hillary Rodham Clinton's pledge this week to oppose Russia's efforts to create alliances of post-Soviet nations as an attempt to "re-Sovietize the region."

"If the U.S. administration wants to have a kind of geopolitical contest with the Russian Federation on the post-Soviet space, I think that the [trade] law will be just the first step in a new crisis, and a serious crisis between Moscow and Washington," Pushkov told The Associated Press.

Moscow's concerns about what it perceives as American meddling into its home turf contributed to a sharp downturn in U.S.-Russia relations under Bush, which hit their lowest point during the August 2008 Russian-Georgian war.

After announcing a policy of "reset" in relations with Moscow in 2009, President Barack Obama signed the landmark New START nuclear arms pact with Russia and encouraged cooperation in other areas. But U.S.-Russia relations later worsened again over Russia's support for the embattled Syrian regime, U.S. missile defense plans and Putin's crackdown on dissent.

Amid the growing strain, Putin accused the U.S. State Department of fomenting massive protests in Moscow against his re-election to a third presidential term in March. The anti-American rhetoric was followed by action.

In September, Moscow ordered an end to the U.S. Agency for International Development's two decades of work in Russia, saying that the agency was using its money to influence elections -- a claim the United States denied. And in another sign of increasing friction with Washington, the Kremlin announced in October that it had no intention of automatically extending a 20-year-old deal with the United States to help secure Russia's nuclear stockpiles.

Washington accuses Moscow of propping up Bashar Assad's regime despite its bloody crackdown on an uprising that began in March 2011.

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Russia and China have used their veto power at the UN Security Council three times to block sanctions against Assad's government, and Moscow has continued to provide Assad with weapons despite strong U.S. protests.

Despite Russian leaders' angry rhetoric, the Kremlin is unlikely to take any anti-U.S. action for fear of causing an even bigger strain in relations, Sergei Alexashenko, an economist who was a deputy chief of Russia's Central Bank, told Ekho Moskvy radio late Thursday.