The company said in a statement it will begin monitoring ads in those two countries immediately "through a combination of automated and human review." It said it will begin enforcing the rules in Singapore and Argentina "within the next few months."
Under scrutiny from regulators since Russia used social media platforms for widespread meddling in the 2016 U.S. presidential election, Facebook has been rolling out ads transparency tools country by country since last year.
The rules - already in place in the United States, the European Union, Britain and India - require ads about politics, elections or "social issues" to be labeled as "paid for" and placed in a publicly searchable archive for seven years, along with information on who saw them and how much they cost.
Facebook said it was making its transparency tools available to advertisers in more than 190 countries, although verification was not yet a requirement in most of those places.
Canadian lawmakers have said the world's major social media companies, including Facebook, were not doing enough to help combat potential foreign meddling in Canada's general election in October.