Chelsea Manning, the US soldier sentenced to 35 years for leaking thousands of classified documents to WikiLeaks, has applied to Barack Obama for a pardon.

The army private, formally known as Bradley Manning, has formally written to the White House asking for a presidential pardon for the conviction for leaking more than 700,000 military and State Department records.

In a written statement to Obama and secretary of the army, John McHugh, Manning said that the classified information was leaked to Julian Assange's website "out of a concern for my country and the world that we live in".

"It was never my intention to hurt anyone. I only wanted to help people" he added.

Manning's leaking of the classified documents, including diplomatic cables and a video of a US helicopter killing civilians, was the largest leak of classified material in US history. Manning received the longest sentence ever for disclosing US government secrets to others for publication.

A court-martial convicted Manning of 20 charges, including espionage and theft. He was acquitted of the most serious charge of aiding the enemy when he was sentenced.

Shortly afterwards, Manning announced his desire to live as a woman named Chelsea. Manning signed the petition with his legal name, Bradley Manning, not Chelsea.

Mannings announced desire to live as a woman following sentence
Mannings announced desire to live as a woman following sentence (Reuters) Reuters

In a covering letter with the request for the pardon, Manning's civilian lawyer David Coombs added: "We rely upon whisteblowers, even in those instances that might cause embarrassment, to keep our government accountable to its people.

"Private Manning is a military whistleblower. He disclosed documents that were vital for a healthy public debate about our conduct in Iraq and Afghanistan, our detention policies at Guantanamo, and our diplomatic activities around the world.

"The sentence given to him by the military judge grossly exaggerates the seriousness of his conduct. The sentence was disproportionate to both the offence and the offender. It will undoubtedly have a chilling effect on future whistleblowers and damage the public's perception of military justice.

In the request, Manning wrote: "I will serve my time knowing that sometimes you have to pay a heavy price to live in a free society. I will gladly pay that price if it means we could have a country that is truly conceived in liberty and dedicated to the proposition that all women and men are created equal."

Obama has received 1,496 petitions for pardons, 39 of which he has granted, according to the Justice Department's Office of the Pardon Attorney.