Facebook Chief Executive Mark Zuckerberg said on a conference call with analysts on Thursday that political advertising on his platform is more transparent than on any other medium.

He said ahead of the presidential election, Facebook ran the largest voting information campaign in U.S. history and estimated that the platform helped 4.4 million people register to vote.

Facebook blocked new political and social ads from running as of Tuesday until after Election Day, Mr. Zuckerberg said. If someone tries to declare victory in an ad, Facebook will put an indication label on the top of the ad noting that the outcome is still undecided.

Next week will certainly be a test for Facebook, Mr. Zuckerberg said, adding that election integrity is and will be an ongoing challenge for his company.