RIGA, Latvia—Latvia's media watchdog suspended the broadcast rights of a Russian-language state television station for three months, citing alleged "war propaganda," and is considering taking action against another Russian-language station.

The moves by Latvia's National Electronic Mass Media Council come as public officials in the former Soviet state are increasingly cracking down on supporters of Russia President Vladimir Putin. A quarter of Latvian residents are ethnic Russians, and more than half of households in Riga, the capital, speak Russian as their primary language—factors that add tension as nearby Ukraine remains in crisis.

This week, Latvian security authorities launched an investigation of Tatjana Zdanoka, a European Parliament member affiliated with a political party that recently renamed itself Latvian Russian Union. Ms. Zdanoka is being investigated in relation to allegations that she is working to undermine the Latvian state in her support for Russia. She has called the allegations "stupid" and billed them as a publicity stunt by a political rival.

The media watchdog said it was suspending Rossiya RTR based on the agency's analysis of news broadcasts between March 2 and March 17 that "justified military aggression against a sovereign state."