Image copyright EPA Image caption Phelps retired after winning an unprecedented 22nd Olympic medal in 2012 but has since returned to action

US Olympic swimmer Michael Phelps has been arrested for driving under the influence, authorities have said.

Police in Baltimore, Maryland, said he was stopped for speeding after being caught going 84mph (135km/h) in a 45mph zone early on Tuesday morning.

Mr Phelps was co-operative but failed a series of standard field sobriety tests, traffic police said in a statement. He was charged and released.

The most decorated Olympian ever, with 22 medals, later apologised on Twitter.

"I understand the severity of my actions and take full responsibility," Mr Phelps wrote.

Image copyright European Photopress Agency Image caption Phelps is the most decorated Olympian in history

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

Mr Phelps, 28, retired after winning his 22nd Olympic medal at the London Games in 2012 but came out of retirement earlier this year.

The Maryland Transportation Authority said Mr Phelps was driving a white 4x4 in Fort McHenry tunnel in Baltimore when the vehicle was caught on police radar at 01:40 local time (05:40 GMT).

Police said he was "arrested and charged with DUI [driving under the influence], excessive speed and crossing double lines".

The statement said Mr Phelps was co-operative throughout the process and was released after being charged.

Mr Phelps, who is from Baltimore County, was previously charged for driving under the influence in Maryland in 2004. He pleaded guilty to driving while impaired in exchange for 18 months' probation.