WASHINGTON, March 24 (Reuters) - Attorneys general for 12 U.S. states on Wednesday accused Facebook Inc and Twitter Inc of doing too little to stop people from using their platforms to spread false information that coronavirus vaccines are unsafe.

In a letter to Facebook Chief Executive Mark Zuckerberg and Twitter CEO Jack Dorsey, the Democratic attorneys general said “anti-vaxxers” lacking medical expertise and often motivated by financial gain have used the platforms to downplay the danger of COVID-19 and exaggerate the risks of vaccination.

They called on both companies to enforce their own community guidelines by removing or flagging vaccine misinformation.

The letter said anti-vaxxers control 65% of public anti-vaccine content on Facebook, Instagram and Twitter, and have more than 59 million followers on those platforms and Google’s YouTube.

It also said some misinformation targets Blacks and other communities of color where vaccination rates are lagging.

“Given anti-vaxxers’ reliance on your platforms, you are uniquely positioned to prevent the spread of misinformation about coronavirus vaccines that poses a direct threat to the health and safety of millions of Americans in our states and that will prolong our road to recovery,” the letter said.

Facebook spokeswoman Dani Lever said the company has removed millions of pieces of COVID-19 and vaccine misinformation, and tries to combat “vaccine hesitancy” by regularly directing users to reliable information from health authorities.

Twitter said it has removed more than 22,400 tweets in connection with its policy toward COVID-19 posts, and prioritizes removing content that could cause “real-world” harm.

Wednesday’s letter was signed by the attorneys general of Connecticut, Delaware, Iowa, Massachusetts, Michigan, Minnesota, New York, North Carolina, Oregon, Pennsylvania, Rhode Island and Virginia.

Zuckerman, Dorsey and Sundar Pichai, the chief executive of Google parent Alphabet Inc, are scheduled to testify on Thursday before two House of Representatives subcommittees about combating online disinformation.

The coronavirus pandemic has sickened more than 124 million people worldwide, and caused more than 2.7 million deaths.