Eight explosions ripped through three churches holding Easter services on Sunday as well as four upmarket hotels in Sri Lanka leaving at least 207 people dead and 450 wounded.
The initial six blasts happened almost simultaneously across the country in Colombo, Negombo (a Catholic majority town north of the capital), and the eastern town of Batticaloa. Hours later, a seventh explosion hit the town of Dehiwala south of the capital. The eighth killed three police officers when they entered a residence in a suburb north of Colombo.
An official says they suspect the earlier blasts at three churches were carried out by suicide bombers.
The country's foreign minister said at least 27 foreigners were among those killed.
Sri Lanka's government imposed a nationwide curfew that police said would go into effect immediately and would last "until further notice", after a string of deadly blasts.
Sri Lanka's defence ministry initially said the curfew would be imposed overnight, but the police subsequently said it would go into effect straight away.
Government officials also said major social media networks and messaging apps, including Facebook and WhatsApp, have been blocked inside the cuntry to prevent misinformation and rumours.
LIVE: Multiple explosions in Sri Lanka
Colombo National Hospital Director Samindi Samrakoon said she knew of at least 137 deaths and 400 people injured.
The fatalities include at least 42 people killed in Colombo, where three hotels and a church were hit, 25 dead in the town of Batticoloa, where a church was attacked and at least 62 in the church attack in Negombo.
It was the worst violence in Sri Lanka since the end of the civil war a decade ago. The magnitude of the bloodshed recalled the random bombings perpetrated by the separatist Tamil Tigers that targeted a bank, a shopping mall, a Buddhist temple and hotels popular with tourists.
In an address, President Maithripala Sirisena said he was shocked by the explosions and appealed for calm.
Finance Minister Mangala Samaraweera, on Twitter, said the attacks had killed "many innocent people" and appeared to be a "well-coordinated attempt to create murder, mayhem & anarchy."
NewFirst, a Sri Lankan based news website said that the public was being asked to donate blood due to a massive demand for transfusions at hospitals treating the wounded.
On the ground, the emergency response is ongoing.
"Our people are engaged in evacuating the casualties," a source in the police bomb squad said.
Sri Lanka’s Minister of Economic Reform Harsha de Silva said there were foreigners among the wounded.
“Please stay calm and indoors. Many casualties including foreigners,” he tweeted.
He said that he had been at the site of the attacks with the Secretary of Defence Hemasiri Fernando and the emergency response was in full swing with teams at all the sites hit.
The MP said that Prime Minister Ranil Wickremesinghe was returning to the capital and there would be an emergency meeting shortly.
The three churches hit were the St. Anthony's Shrine in Colombo; St. Sebastian's Church in Negombo, a Catholic majority town north of Colomb; and the Zion Church in the eastern town of Batticaloa.
Alex Agileson who was in the vicinity of the St Anthony’s Shrine said buildings in the surrounding area shook with the blast.
He said a number of injured were carried in ambulances.
The St. Anthony's Shrine and the three hotels are in Colombo and are frequented by foreign tourists.
The explosion ripped off the roof and knocked out doors and windows at St. Sebastian's, where people carried the wounded away from blood-stained pews, local TV footage showed.
The three hotels believed to have been hit were The Kingsbury; The Shangri-La Hotel; and the Cinnamon Grand, all in Colombo.
In footage on Sri Lankan station Hiru TV, the side one of the high-end hotels hit appeared to be blown out, with shattered glass and rubble strewn across the street outside. It is unclear at this stage which site the casualties are coming in from.
At least one of the victims was killed in Colombo's Cinnamon Grand Hotel, near the prime minister's official residence, where the blast ripped through a restaurant, a hotel official told AFP.
There has so far been no claim of responsibility for the coordinated bombings.
Hours after the blasts, countries around the world began to denounce the attacks.
The UAE Ministry of Foreign Affairs said it stands with the government and people of Sri Lanka in the face of violence and radicalism, state news agency WAM reported. It added that it opposes all forms of violence and terrorism that targets religions and races.
The ministry sent condolences to the families of the victims and wished a quick recovery for the injured.
Pope Francis denounced the "cruel violence" of the Easter Sunday attacks in Sri Lanka and prayed for all those who are suffering from the bloodshed.
Francis added an appeal at the end of his traditional Easter Sunday blessing to address the massacre.
Speaking from the loggia of St. Peter's Basilica, Francis said: "I want to express my loving closeness to the Christian community, targeted while they were gathered in prayer, and all the victims of such cruel violence."
He added: "I entrust to the Lord all those who were tragically killed and pray for the injured and all those who are suffering as a result of this dramatic event."
Meanwhile, the Catholic Church in the Holy Land voiced support for Sri Lanka's Christians.
A statement issued in Jerusalem said the blasts were particularly sad as they "came while Christians celebrate Easter".
"We pray for the souls of the victims and ask for a speedy recovery of the injured, and ask God to inspire the terrorists to repent of their killing and intimidation," the statement said.
"We also express our solidarity with Sri Lanka and all its inhabitants in their various religious and ethnic backgrounds."
US Ambassador to Sri Lanka Alaina Teplitz tweeted her condolences. "Deeply saddened by the senseless attacks in Sri Lanka today. Our thoughts are with the victims and their families. We stand with Sri Lanka’s people at this terrible moment," she said.
UK Foreign Secretary Jeremy Hunt also took to Twitter to condemn the attack. "I’m deeply shocked and saddened by the horrifying attacks on churches and hotels in Sri Lanka today. To target those gathered for worship on Easter Sunday is particularly wicked," he said.