There was still no claim of responsibility for the attacks on two churches and four hotels in and around Colombo, the capital of predominantly Buddhist Sri Lanka, and a third church on the country's northeast coast.
However, a government forensic crime analyst has told the Associated Press that the near-simultaneous attacks were carried out by seven suicide bombers.
Christians celebrate the resurrection of Jesus Christ on Easter Sunday after his death on the cross.
A government source said President Maithripala Sirisena, who was abroad when the attacks happened, had called a meeting of the National Security Council early on Monday. Prime Minister Ranil Wickremesinghe would attend the meeting, the source said.
There were fears the attacks could spark a renewal of communal violence, with police reporting late on Sunday there had been a petrol bomb attack on a mosque in the northwest and arson attacks on two shops owned by Muslims in the west.
Sri Lanka had been at war for decades with Tamil separatists, but extremist violence had been on the wane since the civil war ended 10 years ago.
Out of the country's total population of around 22 million, 70% are Buddhist, 12.6% Hindu, 9.7% Muslim and 7.6% Christian, according to the country's 2012 census.
The island-wide curfew imposed by the government was lifted early on Monday, although there was uncharacteristically thin traffic in the normally bustling capital.
Soldiers armed with automatic weapons stood guard outside major hotels and the World Trade Centre in the business district, where the four hotels were targeted on Easter Sunday, according to a Reuters witness.
Scores of people who were stranded overnight at the main airport began making their way home as restrictions were lifted.
The government also blocked access to social media and messaging sites, including Facebook and WhatsApp, making information hard to come by.
Wickremsinghe acknowledged on Sunday that the government had some prior information about possible attacks on churches involving a little-known Islamist group, but said ministers had not been told.
Sri Lankans accounted for the bulk of the 290 people killed and 500 wounded, although government officials said 32 foreigners were also killed. These included British, US, Turkish, Indian, Chinese, Danish, Dutch and Portuguese nations.
A British mother and son eating breakfast at the luxury Shangri-La hotel were among those killed, Britain's The Telegraph newspaper reported.
One Australian survivor, identified only as Sam, told Australia's 3AW radio the hotel was a scene of "absolute carnage".
He said he and a travel partner were also having breakfast at the Shangri-La when two blasts went off. He said he had seen two men wearing backpacks seconds before the blasts.
"There were people screaming and dead bodies all around," he said. "Kids crying, kids on the ground, I don't know if they were dead or not, just crazy."
Dozens were killed in one of the blasts at the Gothic-style St Sebastian church in Katuwapitiya, north of Colombo. Police said they suspected that blast was a suicide attack.
Three police officers were also killed when security forces raided a house in Colombo several hours after the attacks. Police reported an explosion at the house.
In February-March last year, there were a series of religious clashes between Sinhalese Buddhists and Muslims in the towns of Ampara and Kandy.
On Sunday afternoon, three police officers were killed during a security forces raid on a house in the Sri Lankan capital several hours after the attacks, many of which officials said were suicide bomb explosions. Police reported an explosion at the house.
Thirteen arrests have been made, all of whom are Sri Lankans, police said.
"Altogether, we have information of 207 dead from all hospitals. According to the information as of now we have 450 injured people admitted to hospitals," police spokesman Ruwan Gunasekera told reporters.
Government officials said that 32 foreigners were killed and 30 injured in the explosions that tore through congregations and gatherings in hotels in Colombo, Negombo and Batticaloa.
They included five British people, two of whom had dual US citizenship, and three Indians, according to officials in those countries.
Also among the fatalities were three people from Denmark, two from Turkey, and one from Portugal, Sri Lankan officials said. There were also Chinese and Dutch among the dead, according to media reports.
US Secretary of State Mike Pompeo said US nationals were among those killed, but did not give details.
GOVT HAD 'PRIOR INFORMATION'
There were no immediate claims of responsibility for the attacks in a country which was at war for decades with Tamil separatists until 2009, a time when bomb blasts in the capital were common.
Prime Minister Ranil Wickremsinghe acknowledged that the government had some "prior information of the attack", though ministers were not told.
He said there wasn't an adequate response and there needed to be an inquiry into how the information was used. He also said the government needs to look at the international links of a local militant group.
Agence France Presse reported that it had seen documents showing that Sri Lanka's police chief Pujuth Jayasundara issued an intelligence alert to top officers 10 days ago, warning that suicide bombers planned to hit "prominent churches". He cited a foreign intelligence service as reporting that a little-known Islamist group was involved.
A Sri Lanka police spokesman said he was not aware of the intelligence report.
The Christian community had already felt under pressure in Sri Lanka in recent years.
Last year, there were 86 verified incidents of discrimination, threats and violence against Christians, according to the National Christian Evangelical Alliance of Sri Lanka (NCEASL), which represents more than 200 churches and other Christian organisations.
This year, the NCEASL recorded 26 such incidents, including one in which Buddhist monks allegedly attempted to disrupt a Sunday worship service, with the last one reported on March 25.
The heads of major governments condemned the attacks.
US President Donald Trump said America offered "heartfelt condolences" to the Sri Lankan people and stood ready to help, Indian Prime Minister Narendra Modi said there was "no place for such barbarism in our region", and Turkish President Tayyip Erdogan said the bombings were "an assault on all of humanity".
Pope Francis, addressing people in St Peter's Square, said: "I wish to express my affectionate closeness to the Christian community, hit while it was gathered in prayer, and to all the victims of such cruel violence."
Prime Minister Jacinda Ardern of New Zealand, where a gunman shot 50 people dead in two mosques last month, said in a statement: "Collectively we must find the will and the answers to end such violence."
