With midterm elections in the US and general elections in several other countries knocking at the door, Facebook has rolled out a new tool that makes it easier for researchers and journalists to scrutinise Facebook ads related to politics or issues of national importance.

"We're making advertising more transparent to help prevent abuse on Facebook, especially during elections," Rob Leathern, Facebook's Director of Product Management said in a statement on Wednesday.

Facebook said its new tool, Ad Archive API, would initially be available to a group of publishers, academics and researchers in the US before opening it up more broadly.

"Input from this group will also form the basis of an Archive report that will be available starting in September," Leathern said.

The API offers ad creative, start and end date, and performance data, including total spend and impressions for ads.

It also shows the demographics of people reached, including age, gender and location.

"We're greatly encouraged by trends and insights that watchdog groups, publishers, and academics have unearthed since the archive launched in May. We believe this deeper analysis will increase accountability for both Facebook and advertisers," Leathern said.