President Barack Obama said this evening that former military intelligence analyst Chelsea Manning had served a tough prison term and his decision to commute her 35-year sentence to about seven years served would not signal leniency toward leakers of US government secrets.

Obama told his final news conference as president that he felt it made sense to commute Manning's sentence because she went to trial and took responsibility for her crime.

"I feel very comfortable that justice has been served," Obama said.

Manning gave classified information of more than 700,000 documents, videos, diplomatic cables and battlefield accounts to anti-secrecy group WikiLeaks in 2010, the biggest such breach in U.S. history.

Obama told reporters that Manning had received a "very disproportionate" sentence relative to what other leakers had received.

Obama said the commutation was done without regard to WikiLeaks founder Julian Assange, who said on Twitter last Thursday that if Manning was freed, he would accept extradition to the United States, where there is an open criminal investigation into the activities of WikiLeaks.

"I don't pay a lot of attention to Mr. Assange's tweets," Obama said.

Manning, formerly known as US Army Private First Class Bradley Manning, was born male but revealed after being convicted of espionage that she identifies as a woman. The White House said yesterday that her sentence would end on May 17 this year.

Manning twice tried to kill herself last year and has struggled to cope as a transgender woman in the Fort Leavenworth, Kansas, men's military prison.