WASHINGTON — The Obama administration on Thursday identified 26 additional people and institutions that will be subject to economic sanctions as part of an effort to maintain pressure on the Russian government over its support of insurgents fighting in Ukraine.

The new actions are aimed at individuals or entities that American officials said had been helping previously identified targets to evade sanctions. Eight of the new targets are linked to Gennady Timchenko, a billionaire Russian businessman who is known to have ties to President Vladimir V. Putin.

Also identified as subject to sanctions are four officials who served in the government of former President Viktor F. Yanukovych of Ukraine. Five operators of Crimean ports and one sea ferry operator are also identified. Russia annexed the Crimean Peninsula last year after Mr. Yanukovych was deposed.

“Today’s action underscores our resolve to maintain pressure on Russia for violating international law and fueling the conflict in eastern Ukraine,” said John E. Smith, the acting director of the Office of Foreign Assets Control at the Treasury Department. “Our message is clear: We will continue to act to ensure the effectiveness of our sanctions.”