The swimmer, who came out of retirement this year having hung up his goggles after London 2012, was stopped by police in Baltimore, Maryland.

He was "co-operative" but failed a series of standard sobriety tests, traffic police said in a statement.

Phelps was reportedly driving a 4x4 84mph in a 45mph zone earlier today when he was stopped.

He was charged and released.

Later on Twitter, he wrote in a series of message: "Earlier this morning, I was arrested and charged with DUI, excessive speeding and crossing double lane lines.

"I understand the severity of my actions and take full responsibility.

"I know these words may not mean much right now but I am deeply sorry to everyone I have let down." 

Phelps, who has 22 gold medals to his name, including 18 gold, was previously charged for driving under the influence in Maryland in 2004.

The 29-year-old pleaded guilty to driving while impaired in exchange for 18 months' probation.

In 2009, he was caught on camera smoking from a bong filled with marijuana.

Phelps has yet to make a comment on today's arrest.