Google says it has deleted more than 2,500 YouTube channels tied to China as part of its effort to weed out disinformation on the videosharing platform.

The Alphabet-owned company said the channels were removed between April and June “as part of our ongoing investigation into coordinated influence operations linked to China.”

The channels generally posted “spammy, non-political content,” but a small subset touched on politics, the company said in a quarterly bulletin on disinformation operations.

Google did not identify the specific channels and provided few other details, except to link the videos to similar activity spotted by Twitter and to a disinformation campaign identified in April by social media analytics company Graphika.

The Chinese Embassy in the U.S. didn`t immediately respond to a message seeking comment. Beijing has in the past denied allegations of spreading disinformation.

Disinformation seeded by foreign actors has emerged as a burning concern for American politicians and technologists alike since the 2016 presidential election, when Russian government-linked actors pumped hundreds of thousands of deceptive messages into the social media ecosystem.

Many have spent the past four years trying to avoid a repeat of 2016, with companies like Google and Facebook issuing regular updates on how they`re combating online propaganda.

The bulletin also mentioned activity tied to other countries, including Iran and Russia.