It was supposed to be a joyous Sunday Mass to mark the opening of a new parish church in the northern Tanzanian town of Arusha.
But a bomb exploded killing two people, injuring 60, at least 40 of them seriously.
The attack happened May 5 as parishioners packed in for the beginning of the Mass to officially open Saint Joseph's Catholic parish church.
A top official with the charity Caritas Tanzania was quoted by the Catholic News Agency as saying the on the new parish was the first of its kind for the East African country.
"It is not normal and this has never happened in our country before," Joachim Wangabo, executive secretary of Caritas Tanzania, said in a May 6 interview with CNA.
"The government says it is associated with Muslim terrorists, but it is necessary to know why it happened," he stated.
"This is an act of terrorism perpetrated by a cruel person or group who are enemies of the country," Tanzanian Jakaya President Kikwete said in a statement.
Tanzania has arrested four men from Saudi Arabia and four Tanzanians in connection with the bombing, Reuters news agency reported Monday.
Investigators said they were still determining the type of device used in the attack that took place in the town that is a center for a thriving tourism and safari business to famous locations such as the Serengeti Park.
Eyewitnesses had said the bomb was thrown from a motorcycle into the church.
The Pope's representative to Tanzania, Archbishop Francisco Montecillo Padilla, escaped unhurt from the explosion.
"I would like to express my solidarity to the Archbishop of Arusha and to the whole Catholic community of Arusha, for the very sad event that happened," said Archbishop Padilla.
"The attack should not have happened because it was a celebration of joy, of opening a new church, a new parish," he told Vatican Radio in a May 6 interview.
Tensions have escalated recently between Tanzania's Christian and Muslim communities.
Al Jazeera quoted an angry local lawmaker Godbless Lema saying the blast as the work of "criminals."
"Religious fundamentalism is a reality in this country, but the government does nothing," Lema said outside the church while cordoned off the area and ordered people away from the building.
Tanzania's population of some 45 million is rougly split between Christians and Muslims. It is classified as a least developed country by the World Trade Organization.