WASHINGTON -- A super political action committee supporting Republican presidential candidate Rick Santorum has refunded a $50,000 donation from a London-based securities firm because the contribution could have violated a U.S. law that guards against foreign money in American political campaigns, a spokesman for the group said Tuesday.

The donation returned last month was the first acknowledged evidence of foreign money surfacing in the 2012 presidential race. The concern has worried political observers following a landmark 2010 U.S. Supreme Court decision that removed restrictions on corporate and individual donations to political committees supporting presidential candidates.

Stuart Roy, the spokesman for the Red, White and Blue super PAC, said the $50,000 donation made in January by Liquid Capital Markets Ltd. originated with an American executive at the firm. The money was returned, Roy said, because the donation was mistakenly drawn from the foreign firm's accounts.

Under U.S. law, foreign corporations, individuals and governments have been prohibited since 1966 from providing funds for national elections – a ban the Supreme Court upheld earlier this year.

But the court's earlier ruling in the case of Citizens United enabled U.S. corporations and other well-financed donors to give money to political committees that avoid direct coordination with individual campaigns. Later rulings gave these super PACs more latitude by allowing donors to make unlimited donations with minimal disclosure, which spurred alarm about hidden donations from foreign sources.

The Associated Press reported less than two weeks ago, before the disclosure about the $50,000 refund, on growing concerns among election law experts about the prospect of illegal foreign donations because of the massive amounts of money flowing to the super PACs and lax oversight of disclosure. One Federal Election Commission member, Cynthia L. Bauerly, warned of the potential for circumventing existing rules.

Roy said the $50,000 donation was proposed by an American executive at Liquid Capital Markets in London. Roy said the executive informed super PAC officials he intended to make the donation then mistakenly provided the money from the firm's accounts – which would have violated the ban on foreign money.

Red, White and Blue's officials noticed the discrepancy and quickly returned the donation, Roy said.

"We had spoken to one of the executives there who's an American citizen," he said. "But instead of sending the money himself, he sent it from the company."

Roy did not identify the executive, but Liquid Capital Market's website describes its CEO, Chris Siepman, and his brother, Gregg Siepman, a co-founder of the company, as Americans. There was no immediate response to attempts by the AP to reach Chris Siepman or other Liquid Capital officials.