The clarification came hours after Benedict's biographer, Peter Seewald, sparked alarm by telling the Passauer Neue Presse that he had found the 93-year-old ex-pope exceptionally frail when he visited him on Saturday.

Seewald said Benedict, who has been in shaky health for some time, was now suffering from shingles, a viral infection that causes painful rashes and is common among older people.

"The health conditions of the Pope Emeritus are not particularly worrying, apart from being those of an old man of 93 who is overcoming the most acute phase of a painful but not grave illness," the statement said.

Seewald said Benedict's voice was barely audible - echoing something other visitors have said for months - and that the former pope told him he might pick up writing again if he regains his strength.

In June, Benedict, who lives in a former convent in the Vatican gardens, left Italy for the first time since his resignation in 2013 for an emotional farewell visit to his older brother Georg in their native Bavaria.

Georg Ratzinger died on July 1 aged 96.

The two brothers were ordained priests on the same day in 1951.

Benedict, who was elected in 2005 to succeed the widely popular Pope John Paul II after a reign of nearly 27 years, shocked the world and even his closest aides on February 11, 2013, when he announced in Latin he was stepping down.

He told a gathering of cardinals that he was too old and frail to lead an institution with more than 1.3 billion members.

Australian Associated Press