US swimmer Ryan Lochte has apologised for his behaviour surrounding a late-night incident at a Rio de Janeiro petrol station, saying he should have been more careful and candid about how he described what happened.

Lochte said in a lengthy post on Instagram that he was apologising for his role in taking the focus away from other Olympic athletes.

The 12-time gold medallist reiterated his view that a stranger pointed a gun at him and demanded money to let him leave.

https://t.co/n82dZH2gfl pic.twitter.com/rGp1nmA94G

— Ryan Lochte (@RyanLochte) August 19, 2016

But Lochte said he should have handled himself more responsibly.

Brazilian police have said Lochte lied by saying he and three other swimmers were robbed.

They vandalised a petrol station bathroom and were confronted by security guards, police said.