For the first time, Mitt Romney, the likely U.S. Republican presidential nominee, has surged ahead of President Barack Obama in campaign fundraising.
Figures released by Mr. Romney's campaign show the former Massachusetts governor and the Republican National Committee (RNC) raised more than $76 million in May.
President Obama and his Democratic allies say they brought in more than $60 million last month.
In a statement released by Mr. Romney's campaign, RNC chairman Reince Priebus says the group's strong fundraising is an indication that voters are "tired of President Obama's broken promises" and are seeking change.
President Obama's office thanked donors, but provided no immediate reaction to the Republican figures. Mr. Obama travels to the U.S. west coast on Thursday for a fundraising event in Los Angeles.
Later, he delivers remarks on college affordability in Las Vegas.
Mr. Romney secured his nomination in May with a victory in the Texas primary that gave him more than the required 1,144 delegates.
Some information for this report provided by AP, AFP and Reuters.