Sri Lankan officials say the terrorist attack that killed 290 people, including two Australians, was carried out with the support of an worldwide network.
On Monday, another blast rocked a street near a church in the capital, Colombo.
The three hotels hit were the Shangri-La Colombo, Kingsbury Hotel and Cinnamon Grand Colombo.
The fact that these attacks successfully targeted five star hotels located in Sri Lanka's commercial capital, which are expected to be well-guarded, shows that security of "these areas could still be breached", she noted.
The hotel said several guests and three employees were killed.
Rajitha Senaratne, the Sri Lankan health minister, told reporters he believes a group of extremists called National Thowheeth Jamaath was responsible, along with the "international network" of terror "without which these attacks could not have succeeded". "Compared with similar attacks in the Middle East and Southeast Asia, it has the DNA of attacks carried out by Islamic State [Daesh] and al Qaeda", said Alto Labetubun, an anti-terrorism expert who has researched the two groups for a decade.
A later statement said President Maithripala Sirisena would ask for foreign help to track down the global links to the attackers.
Demanding serious action as to why the warning was ignored, Minister of Telecommunication of Sri Lanka Harin Fernando said, "Some intelligence officers were aware of this incident".
There are no reports of Canadians among the estimated 39 foreigners killed in the explosions.
"If that (bomb) was two seconds later, she would have been dead". The explosions at the fourth hotel and the house were in the afternoon.
Danish billionaire Anders Holch Povlsen lost three children in the Sri Lanka bombings, according to multiple media reports.
Canadian officials warn that the situation remains volatile with a risk of further attacks throughout Sri Lanka.
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The government announced a curfew in Colombo from 8 p.m. until 4 a.m.
Calling for the resignation of the Inspector General of Police, Senaratne said: "This morning (Monday) the President, the Prime Minister and State Defence Minister met for the first time".
The attacks have raised fears of a resurgence of the communal violence that has often plagued the island.
Sunday's attacks were the deadliest in Sri Lanka since the end of the country's civil war in 2009.
Sri Lanka's 22 million people include minority Christians, Muslims and Hindus.
President Sirisena said in a statement that the government would seek foreign assistance to track any overseas links.
An improvised explosive device - a 6ft-long [1.8m] plastic pipe packed with explosives - was also found and defused near the airport in Colombo.
"We are in the position of healing our wounds after a 30-year war", he said in an interview. Local authorities have also temporarily blocked access to some social media.
Sam wasn't hurt, thankfully, telling 3AW he was about "5 to 10 metres away" from the initial blast.
He said he and a travel partner were having breakfast at the Shangri-La when two blasts went off.
Footage on CNN showed what it said was one of the bombers wearing a heavy backpack. Pictures showed bodies on the ground and blood-spattered pews and statues. The man patted a young child on the head before entering the Gothic-style St. Sebastian church in Katuwapitiya, north of Colombo. "Neither I nor the ministers were kept informed".