At least 207 people have been killed in a series of Easter Sunday explosions targeting churches and hotels in Sri Lanka.
A police spokesperson said that more than 450 people have been injured.
Six sites were hit with near-simultaneous explosions, with officials saying two smaller blasts followed a few hours later.
The Shangri-La, Kingsbury and Cinnamon Grand Hotels, all in Colombo, were targeted.
Three churches in Negombo, Batticaloa and Colombo's Kochchikade district were also hit during Easter services.
A senior official told the Associated Press at least two of the blasts were suspected to have been caused by suicide bombers.
Local media are reporting seven arrests have been made following a raid on a house in the capital.
According to the country's junior defence minister, three officers were killed during the raid.
No one has yet said they are behind the attacks, which are the worst violence in the country since Sri Lanka's bloody civil war ended a decade ago.
At St Sebastian's Church in Negombo, people carried the wounded away from blood-stained pews after the explosion ripped off the roof and knocked out doors and windows.
The church has appealed for help on its Facebook page.
The Sri Lankan government has declared a curfew with immediate effect, and has shut down access to social media and messaging services.
Advice for Irish citizens
The Department of Foreign Affairs has advised Irish citizens to follow the instructions and advice of local authorities, and stay indoors where possible.
The Irish embassy in India, which is accredited to Sri Lanka, has said it is aware of the incidents.
Those who require consular assistance are advised to call the New Delhi embassy on +91-114-9403-200.
Ireland also has an Honorary Consulate in Colombo on +94-(11)-258-7895 or the Department of Foreign Affairs in Dublin can be contacted on +353-1-408-2000.
You can also call our Honorary Consulate in Colombo on +94 (11) 258 7895 and the Department of Foreign Affairs in Dublin on +35314082000
— Irish Embassy India (@IrlEmbIndia) April 21, 2019
President Michael D Higgins said: "As President of Ireland, I am sure that people in Ireland will have heard with great concern of the heavy loss of life that has happened at places of worship in Sri Lanka, at a time of religious significance.
"The right to the freedom of worship is a fundamental right.
"To the families of those who died and those who have been injured I send the sympathies and solidarity of the people of Ireland."
"The right to the freedom of worship is a fundamental right."
Statement by President Higgins on the attacks in Sri Lanka: https://t.co/pHuAhKYLem
— President of Ireland (@PresidentIRL) April 21, 2019
Tánaiste and Foreign Affairs Minister Simon Coveney has condemned the attacks.
He also expressed Ireland's solidarity with the people and government of Sri Lanka "at this tremendously difficult time."
He said: "I am shocked at the appalling attacks on innocent civilians this morning in Sri Lanka.
"No political or other cause can justify or excuse the bombing of people at worship or simply going about their daily lives.
"I express my sympathy to the families of those who have been killed and my support to those who have been injured.
"On behalf of the government of Ireland I also express our solidarity with the people and government of Sri Lanka at this tremendously difficult time.
"Ireland strongly supports everyone's freedom of religion and belief.
"Attacks such as those in Sri Lanka today and in Christchurch and elsewhere are a challenge to us all to do everything that we can to defend that right. Places of worship must be places of peace, free from fear."
Sri Lankan Prime Minister Ranil Wickremesinghe said: "I strongly condemn the cowardly attacks on our people today.
"I call upon all Sri Lankans during this tragic time to remain united and strong.
"Please avoid propagating unverified reports and speculation. The government is taking immediate steps to contain this situation."
India's Prime Minister Chowkidar Narendra Modi tweeted: "Strongly condemn the horrific blasts in Sri Lanka.
"There is no place for such barbarism in our region. India stands in solidarity with the people of Sri Lanka.
"My thoughts are with the bereaved families and prayers with the injured."
Strongly condemn the horrific blasts in Sri Lanka. There is no place for such barbarism in our region. India stands in solidarity with the people of Sri Lanka. My thoughts are with the bereaved families and prayers with the injured.
— Chowkidar Narendra Modi (@narendramodi) April 21, 2019
Pakistan's Prime Minister Imran Khan also condemned the "horrific terrorist attack".
"Pakistan stands in complete solidarity with Sri Lanka in their hour of grief", he said.
Australian Prime Minister Scott Morrison condemned "the devastating & horrific Easter terrorist attacks on innocents in churches & hotels".
Additional reporting: Jack Quann