The 73-year-old Italian prelate had undergone lung surgery nearly three weeks ago and had been on assisted ventilation for much of his postoperative care.
Archbishop Sambi, whose title was apostolic nuncio, was one of Pope Benedict XVI's first major appointees and had served in the U.S. post since 2006. He fell ill when he was preparing to return to Rome, where it was widely expected he would be named a cardinal.
He had worked closely with the U.S. Conference of Catholic Bishops, and he made many recommendations on which priests should be elevated to leadership roles, including Archbishop Edwin F. O'Brien of Baltimore.
In a statement Thursday, Archbishop O'Brien called his death "a great loss for the Catholic Church, especially here in the United States. Both as a diplomat and a priest, Archbishop Sambi excelled through his gentle spirit and infectious goodness, and the impact of his work as apostolic nuncio to the United States will be felt for many years to come.
"A churchman who served us with extraordinary spiritual insights, boundless physical energy and a compassionate generosity that reached out in all generations, Archbishop Sambi has been a great model to so many of us," Archbishop O'Brien said.
In a diplomatic career that spanned 40 years, Archbishop Sambi had served twice as Vatican ambassador to Israel and once in Indonesia. In his U.S. role, Archbishop Sambi "enjoyed the highest respect and deepest affection of the bishops of the United States and of our Catholic people," Archbishop Timothy M. Dolan, president of the U.S. Conference of Catholic Bishops, said in a statement. He called Archbishop Sambi "a friend of the United States in so many ways."
Archbishop Sambi helped coordinate the pope's 2008 visit to the U.S., and he traveled widely throughout the country, often to attend the ordination of bishops. He also participated in the November 2006 dedication of Baltimore's Basilica of the National Shrine of the Assumption, the nation's first cathedral, and spoke often to the U.S. Bishops Conferences in Baltimore.
Archbishop Sambi "was well regarded in this country and exceptionally beloved," said Rocco Palmo, a Catholic journalist based in Philadelphia. "He had been unusually present for a nuncio, not just at official functions. He made a point of seeing the country."
Ken Hackett, president of Baltimore-based Catholic Relief Services, said the organization worked closely with the archbishop during his tenure in Israel. "His heart was with the all of the people in the region, and his dream was one of peace in the Holy Land," he said. "He was a good friend and a great supporter of the charitable mission of the Church."
Archbishop Sambi understood and loved America and was always eager to meet its people, said Archbishop Dolan of New York. He also was a friend of the media, whom he considered the conveyors of truth and the representatives of the American people, Archbishop Dolan said.
"He enjoyed everything from a stroll in the park near his residence in Washington to the diplomatic functions he attended as part of his service as the representative of the Holy See," Archbishop Dolan said.