WASHINGTON — Underlying talk about taking harsh punitive measures against Russia for its military incursion into Ukraine are economic complications and worries that sanctions levied against Moscow could backfire on the U.S. and Europe.

Heavier U.S. and European Union sanctions could sting Russia’s already slow-growing economy and hurt its financial sector. But Moscow could retaliate and seize American and other foreign assets or cut exports of natural gas to Europe, which is heavily dependent on Russia for energy.

Declaring his determination not to let the Kremlin carve up Ukraine, President Barack Obama on Thursday slapped new visa restrictions on Russian and other opponents of Ukraine’s government in Kiev and authorized wider financial penalties against those involved in the military intervention or in stealing state assets. Obama emphasized his resolve in an hourlong telephone call with Russian President Vladimir Putin, affirming his contention that Russia’s actions violate Ukraine’s sovereignty.

On Capitol Hill, both chambers of Congress looked to advance legislation imposing hard-hitting sanctions on Russia.

Obama hailed U.S. cooperation with the European Union, which on Thursday suspended talks with Putin’s government on a wide-ranging economic agreement and on granting Russian citizens visa-free travel within the 28-nation bloc. But Europe’s presidents and prime ministers remain divided on taking more drastic steps such as freezing assets and issuing travel bans on Russian officials.