Pope Benedict XVI's efforts to unify the Catholic Church and reach out to Christian traditionalists took a new step Monday with the start of talks between the Vatican and a group of breakaway Catholics that includes a Holocaust denier.

The Vatican said the three-hour talks with a delegation from the Society of St. Pius X were held in a "cordial, respectful and constructive climate" and would continue frequently over the coming months.

The society, founded by the late ultraconservative Archbishop Marcel Lefebvre, split from Rome over the modernizing reforms of the Second Vatican Council, particularly its outreach to Jews and Christians who were not Catholics. Pope Benedict XVI's effort to reconcile with the group is part of his overall aim of unifying the church and putting a highly conservative stamp on it. Just last week, he made a major gesture in that direction by making it easier for Anglican traditionalists to convert to Roman Catholicism.

A Vatican spokesman, the Rev. Federico Lombardi, said the meeting marked "the beginning of a new phase of relations" and there was a "sense of trust for the meeting and its prospects" that hadn't existed before.

Lefebvre founded the Swiss-based society in 1969, opposed to Vatican II's reforms which revolutionized the church's relations with Jews and allowed for the celebration of Mass in the vernacular rather than Latin.

In 1988, the Vatican excommunicated Lefebvre and four of his bishops after he consecrated them without papal consent.

Benedict has worked for two decades to bring the group back into the Vatican's fold. In 2007, he relaxed restrictions on celebrating the old Latin Mass, which the traditionalists had demanded. In January, he accepted another one of their demands by approving a decree lifting the bishops' 1988 excommunications.

But on the same day the Vatican decree was signed, British Bishop Richard Williamson was shown on Swedish state television saying historical evidence "is hugely against 6 million Jews having been deliberately gassed" during World War II.

The outcry was immediate, with both Jews and members of the Catholic hierarchy criticizing the pope's rehabilitation of a Holocaust-denier. While condemning Williamson's remarks, the Vatican defended its decision, only saying later that it hadn't known about his very public views about the Holocaust.

The Vatican has set out particular conditions for Williamson to be fully brought back in, saying he must "absolutely and unequivocally" distance himself from his Holocaust remarks, if he ever wants to be a prelate in the church. Williamson has apologized for causing scandal to the pope but hasn't publicly repudiated his views.

Monday's Vatican statement said the two sides identified the outstanding doctrinal differences between them that would be discussed in future meetings. The issues include the principles of ecumenism and the relationship between Christianity and non-Christian religions.

Lombardi said the next meeting is expected in January, and that talks will take place roughly every two months.

Such an intense workload "shows that they want to go ahead with a certain amount of determination," Lombardi said.

Prior to the start of talks, the society's delegation leader, Bishop Alfonso de Galarreta, had said negotiations may take years.

There was no immediate comment from the society.

The Vatican has said the society's members must "fully recognize" Vatican II as well as the teachings of all the popes who came after it, if they want to be fully reintegrated into the Church.

The society says it is upholding true Catholic tradition by rejecting elements of Vatican II's teachings, and says the Church's current problems, including a shortage of priests, are a direct result of the 1962-65 meetings.

Lombardi said that among the issues discussed was the concept of tradition.

The Rev. Robert Gahl, professor of moral philosophy at the pontifical university of the Holy Cross, said "some of these Lefebvrites understand tradition as a way that everything has to be fixed exactly the way it was back in the past, using the same words in the liturgy, celebrating Mass with the same gestures."

"Instead Pope Benedict says we need to celebrate Mass with continuity with the past, with that tradition, but there can be changes that are dynamic, just like a living organism," he told Associated Press Television News.