KIEV, Ukraine  A year after taking office with a vow to pursue close ties to Russia, the Ukrainian president is overseeing a broad crackdown on the pro-Western opposition that mirrors the kind of pressure tactics used by his allies in the Kremlin.

Prosecutors appointed by the president, Viktor F. Yanukovich, are carrying out many investigations of opposition leaders, including the former prime minister, Yulia V. Tymoshenko, who was a hero of the Orange Revolution of 2004.

The United States and European Union, which had held up Ukraine as a post-Soviet model for relatively fair elections and the peaceful transfer of power between political parties, have expressed growing alarm over the Yanukovich government’s conduct.

Ms. Tymoshenko has been repeatedly interrogated by prosecutors who said they were examining official corruption during her tenure as prime minister. But so far they are focusing on an accusation that has not aroused much public outrage: they say she violated the law in 2009 by shifting hundreds of millions of dollars from environmental funds to pay pensions. (She is not accused of personally stealing any of the money.)