Facebook said it removed campaign ads for President Donald Trump which appeared to stoke fear by claiming that his Democratic rival Joe Biden would pose threats by allowing more immigration.

The move late Wednesday marked the latest by the leading social network seeking to curb misinformation while seeking to steer clear of political involvement.

The messages, which remained visible in the Facebook ad library, said Biden was “dangerous for America” and claimed the Democrat would allow a “surge” in immigration, suggesting this could increase coronavirus and security risks.

“We rejected these ads because we don’t allow claims that people’s physical safety, health, or survival is threatened by people on the basis of their national origin or immigration status,” Facebook said in a statement.

The ad rejection underscored the challenge for social platforms seeking to sift through mountains of false claims during a heated election campaign, many of which come from Trump.

Facebook earlier this year removed a Trump ad which contained a symbol used in Nazi Germany to designate political prisoners.

Separately, Facebook also said it was clarifying its rules on ads seeking to question the legitimacy of the electoral process amid the latest Trump comments suggesting he may not trust the ballot count.

“In addition to banning ads that make premature declarations of victory, we also won’t allow ads with content that seeks to delegitimize the outcome of the US election,” Facebook product manager Rob Leathern said.

“This would include calling a method of voting inherently fraudulent or corrupt, or using isolated incidents of voter fraud to delegitimize the result of an election.”