Pope Francis has disclosed that he may step down if he becomes too tired to continue in the role.

Asked by Italian media what would lead him to resign, the Pope, 86, warned of 'a fatigue that makes you not see things clearly... A lack of clarity when it comes to knowing how to assess situations.'

He said that he was 'a bit ashamed' to use a wheelchair due to a knee injury.

'I am old. I have less physical resistance, the knee [problem] was a physical humiliation, even if the recovery is going well now.'

Last month, the Pope said that papal resignations should happen in exceptional circumstances, and said quitting was not 'on [his] agenda'.

Pope Francis has been head of the Catholic Church since March 2013, on Monday marking 10 years of his papacy.

In an interview with Italian Swiss television RSI, with extracts published in La Repubblica, La Stampa, and Corriere della Sera, he also said that the war in Ukraine had been driven by the interests of several empires.

He said the conflict was fuelled by 'imperial interests, not just of the Russian empire, but of empires from elsewhere.'

He expressed a readiness to talk to Russian President Vladimir Putin to call for peace.

While the Pope has repeatedly called for an end to the war and denied being pro-Putin he has previously suggested the invasion of Ukraine was 'perhaps in some way provoked'.

Asking himself in June last year whether this made him a supporter of Putin, he said: 'No, I am not. It would be simplistic and wrong to say such a thing.' He added: 'I am simply opposed to reducing complexity to distinction between good and bad'.

The Pope denounced the injustice of war at the Christmas Eve mass last year from a wheelchair.

The congregation was there warned that the Pope was unable to stand for long periods of time due to pain in his knee.

The leader of the Catholic Church has for over a year suffered with pain in his right knee.

Despite last month saying quitting was not on the agenda, the Pope has progressively added to speculation that he would at some point stand down from his position should his health worsen.

He previously claimed to have signed a resignation letter in case of a deterioration of his health: 'In practice, there is already a rule. I have already signed my renunciation.'

'I signed it and said, "If I should become impaired for medical reasons or whatever, here is my resignation. Here you have it,"' he said, referring to Cardinal Bertone, to whom the letter was given.

In January, he gave a sermon on the 'virtue of stepping aside at the right time'.

He said: 'It is easy to become attached to roles and positions, to the need to be esteemed, recognised and rewarded.'

He continued: 'It is good for us too to cultivate, like [Saint] John [the Baptist], the virtue of setting ourselves aside at the right moment, bearing witness that the point of reference of life is Jesus.