American prosecutors have filed fresh conspiracy and money laundering charges against 16 parents accused of paying bribes to secure places for their children in elite universities.

It is the largest college admissions scam uncovered in US history.

Full House actor Lori Loughlin and her fashion designer husband Mossimo Giannulli were among those parents already charged with racketeering conspiracy for their alleged role in the scheme, in which parents paid about $US25 million ($A35.2 million) in bribes to secure their offspring places at universities including Yale, Georgetown and the University of Southern California.

On Monday, 14 parents, including Desperate Housewives star Felicity Huffman, pleaded guilty to involvement in the scam, masterminded by California college admissions consultant William “Rick” Singer.

Huffman, who faces jail as a result, apologised for the “pain” her actions caused. She insisted her plan to cheat on the SAT test to get her daughter a higher score was concocted without the 18-year-old’s knowledge.

“In my misguided and profoundly wrong way, I have betrayed her,” she said outside court. “This transgression toward her and the public I will carry for the rest of my life.”

Felicity Huffman could go to jail for between four and 10 months. Photo: Getty

Huffman, 56, faces up to 20 years in prison but prosecutors have agreed – as part of a plea deal – to recommend jail time at the “low end” of the sentencing range, reportedly four to 10 months.

Loughlin, 54, who has not admitted any involvement, may face a longer sentence. She has also been charged for allegedly giving $500,000 to say her daughters were part of a rowing team, when that was not true.

Singer last month admitting facilitating the cheating scam and bribing coaches to present the parents’ children as fake athletic recruits.

Prosecutors have not yet charged any applicants and said that in some cases the parents involved took steps to try to prevent their children from realising they were benefiting from fraud.

Colleges have begun revoking the admissions and pursuing expulsion of students who obtained their seats as a result of the fraud.

-with AAP