Former Secretary of State and first lady Hillary Clinton announcing a new initiative between the Clinton Foundation, United Nations Foundation, and Bloomberg Philanthropies, titled Data 2x, on December 15, 2014 in New York City. Andrew Burton/Getty Images Hillary and Bill Clinton earned over $25 million for delivering more than 100 speeches since 2014, according to financial disclosure forms released by the Clinton campaign.

Hillary Clinton, the front-runner for the Democratic presidential nomination in 2016, also earned $5 million in royalties for her book, "Hard Choices," which was released in June, according to the forms.

The Clintons' income puts them at least in the top 0.1% of the US population, the Journal reported.

Economic inequality has been a top campaign theme for Democrats for the past several years and Clinton in April voiced concern about the hefty paychecks of some corporate executives in an email to supporters.

But the Clintons themselves have faced criticism for high speaking fees, which for Hillary Clinton have gone up to $250,000 since she left the helm of the State Department in 2013. Liberals have criticized her for taking money from financial institutions, including Goldman Sachs, for speeches they say make her beholden to big business.

Last year, Hillary Clinton was criticized for saying she and her husband were "dead broke" when they left the White House in 2001, even though Bill Clinton made millions of dollars giving speeches after his presidency.

Republican presidential contender Marco Rubio also filed disclosure forms with the Federal Election Commission, the Washington Post reported.

Former President Bill Clinton. Reuters//Brendan McDermid

They show the senator from Florida owes at least $450,000 and as much as $1 million on three mortgages, including a home equity line of credit, the newspaper said.

His assets, which include checking and savings accounts, college funds for his children, and a rental property in Tallahassee, are worth between $361,018 and $1,035,000.

Presidential candidates are required to file the financial information with the FEC within 30 days of declaring their candidacy, although they can seek up to two 45-day extensions.

Republican candidates Senators Ted Cruz of Texas and Rand Paul of Kentucky sought extensions rather than file on Friday, the Post reported.

(Editing by Doina Chiacu)