BANGKOK — A court in central Vietnam convicted 14 democracy activists Wednesday of plotting to overthrow the government and sentenced them to prison terms ranging from three to 13 years in what ­human rights groups said was the largest subversion case to be brought in years.

The defendants are bloggers, writers, and political and social activists who were ­accused of links to a banned prodemocracy group based in the United States that the government accuses of seeking to overthrow it.