Vatican City -- Pope Benedict XVI on Thursday admitted mistakes in the handling of a Holocaust-denying bishop, but said he had been hurt by attacks made on him over the affair.

The pope suggested in a letter to Catholic bishops around the world that the Vatican was unaware of Richard Williamson's claims that no Jews were killed in Nazi gas chambers, and should have consulted the Internet before deciding to lift his ex-communication.

"I have been told that consulting the information available on the Internet would have made it possible to perceive the problem early on," Benedict said in the letter.

The German pontiff regretted that the "extent and limits" of his "discreet gesture of mercy" to Williamson were "not clearly and adequately explained" at first.

He stressed however that while the bishops have been "invited" back into the fold, they "do not (yet) legitimately exercise any ministry in the Church."

The 81-year-old pontiff, who was to visit Israel and the Palestinian territories in May, thanked "Jewish friends" who helped clear up the "misunderstanding" and "restore an atmosphere of friendship and trust."

Also Thursday, the pope met the Shear-Yashuv Cohen, the Grand Rabbi of Haifa, who thanked Benedict for "clearly" condemning Holocaust denial after the Williamson affair erupted.

The delegation had angrily called off the meeting in late January because of the controversy.

In his letter to the bishops, Benedict also expressed his personal anguish at becoming the target of "open hostility" from within the Church over the move.

"I was saddened by the fact that even Catholics who, after all, might have had a better knowledge of the situation, thought they had to attack me with open hostility," he wrote.

Urging Catholics to show unity, Benedict quoted the Apostle Paul's Letter to the Galatians: "If you bite and devour one another, take heed that you are not consumed by one another."

He wrote: "Sad to say, this 'biting and devouring' also exists in the Church today, as expression of a poorly understood freedom."

Benedict's predecessor Pope John Paul II excommunicated Williamson and three other bishops after traditionalist leader Marcel Lefebvre ordained them as bishops of his separatist church in 1988.

Their fraternity rejected reforms passed by Second Vatican Council in the early 1960s, notably including a declaration, Nostra Aetate, which ended a Church doctrine by which the Jews were held responsible for killing Jesus Christ.

"Some groups... openly accused the pope of wanting to turn back the clock to before the Council," Benedict wrote.

Williamson has apologised to anyone offended by his remarks but has refused to retract them, saying only that he would reexamine the historical evidence.

The pope has said previously that he was not aware of Williamson's comments in an interview broadcast on Swedish television in January, that "200,000 to 300,000 Jews perished in Nazi concentration camps, but none of them by gas chambers."

The prelate had made similar assertions in the past, dismissing records of millions killed in gas chambers as "lies, lies, lies."

German Chancellor Angela Merkel led political condemnation of the lifting of the excommunication, also denounced by many European bishops and cardinals.

Vatican spokesman Federico Lombardi said in a statement that the pope had never expressed himself "in such as personal and intense way" before during his papacy, and that the letter should be accorded "maximum attention."

Gina Doggett/AFP/Expatica