A priest in charge of bringing Polish pilgrims to the Vatican was a secret communist informer during the era of Pope John Paul II, it has been alleged.
Father Hejmo described the allegations as 'absurd'
Father Konrad Stanislaw Hejmo, 69, was said to have collaborated with the secret services in communist Poland during the 1980s.
The allegations have been made by a Polish institute investigating Nazi and communist crimes in Poland.
Father Hejmo called the claims "absurd" in a telephone call to Polish state TV.
He also told reporters at Rome airport he was flying back to Warsaw.
Italy's Ansa news agency said he had been in St Peter's Square earlier on Wednesday with 2,000 Polish pilgrims hoping to see Pope Benedict XVI.
Correspondents say that Father Hejmo had limited access to the Pope himself, but may have relayed information to the communist secret service about the pilgrims during the 1980s.
Leon Kieres, head of the Polish Institute for National Remembrance, said they had files stating that Father Hejmo, "was a member of the secret services in communist Poland during the 1980s".
He reportedly used the pseudonyms 'Hejnal' and 'Dominik' for his work.
The files were "convincing and shocking", said the priest's Dominican superior, Father Maciej Zieba, who had seen the documents.
But one Church official, Bishop Tadeusz Pieronek, warned against jumping to hasty judgements.
"We are still not sure of the type of the co-operation, whether he was simply talking about the Holy Father with the secret services or was actually providing secret information on him," he told the Associated Press.
"If he was providing information, then this would be very sad truth."
Pope John Paul II, who died on 2 April, was a critic of communism and is widely seen as helping to bring about its demise in eastern and central Europe.