Rajitha Senaratne, the country's health minister and a spokesman for its Cabinet, said international intelligence agencies had informed Sri Lankan counterparts on April 4 that churches and tourist destinations were being targeted. Five days later, police were given the names of suspects behind the plot.
A wave of near-simultaneous explosions carried out by seven suicide bombers hit three churches and three luxury hotels on Sunday, officials said. Police later reported two further blasts. A minivan exploded in Colombo on Monday, as bomb squad officials were trying to defuse it. No injuries were immediately reported.
Around 500 people were injured and at least 27 foreign nationals were among the dead.
Hemasiri Fernando, the chief of staff to Sri Lankan's president, also told NBC News that the country's security agencies had been alerted in advance.
"We never expected it to be so big," Fernando said. "We never thought it would happen so soon."
Senaratne blamed National Thowheed Jamath, a local Islamist group, for the attacks.
Blasts occurred at St. Anthony's Shrine in Colombo; St. Sebastian's Church in Negombo, a Catholic majority town north of Colombo; and a church in the eastern town of Batticaloa.
The targeted hotels included the Shangri-La Colombo, Kingsbury Hotel and Cinnamon Grand Colombo — all popular with foreign tourists.
Around 22 million live in Sri Lanka. Around 70 percent of the population is Buddhist, 12.6 percent is Hindu, 9.7 percent is Muslim and 7.6 percent is Christian, according to the country's 2012 census.
Mathew Schmalz, a religious studies professor at The College of the Holy Cross in Worcester, Massachusetts, said there isn't a history of tension between Christians and Muslims on the island nation.
However, he said, religious extremism among the Buddhist community has been on the rise in the decade following the end of Sri Lanka's civil war.
"I think extreme Buddhism has tried to fill the void in Sri Lankan society for a sense of identity," Schmalz said, adding that it may have had a "domino effect" and prompted extremism among other groups.
Both Muslims and Christians have been subject to persecution, which is seen as inconsistent with the country's identity, according to Schmalz. There have even been demonstrations against the sale of halal food that adheres to Islamic dietary restrictions.
The group blamed by Sri Lanka's government for the attack has been linked to vandalism of Buddhist statues in the past, according Frederica Jansz, an expert witness specializing in Sri Lankan asylum cases in Britain's courts.
Jansz added that the group had never previously been implicated in any deaths.
Bill Neely and Shammas Ghouse reported from Colombo, and Linda Givetash from London.
Bill Neely is NBC News' chief global correspondent. He joined NBC News from Britain’s ITV News in January 2014. His reports from across the globe have earned many awards, including an unprecedented three consecutive BAFTAs, the British equivalent of the Oscars, for his work in China, Haiti, and the U.K.
Linda Givetash is a reporter based in London. She previously worked for The Canadian Press in Vancouver and Nation Media in Uganda.
Shammas Ghouse is a journalist based in Sri Lanka.