A previously little-known local group carried out the attacks, Sri Lankan authorities believe.

Cabinet spokesman Rajitha Senaratne said the Islamist group National Towheed Jamath (NTJ) were thought to be behind the killings.

Mr Senaratne said earlier that they believed the group had international help.

Police in Colombo have recovered 87 low-explosive detonators, external from the Bastian Mawatha Private Bus Station in Pettah, the BBC's Azzam Ameen reports.

Sri Lankan President Maithripala Sirisena will ask for foreign assistance to find the international links to Sunday's attacks.

"The intelligence reports (indicate) that foreign terrorist organisations are behind the local terrorists. Therefore, the president is to seek the assistance of the foreign countries," his office said in a statement.

Cabinet spokesman Rajitha Senaratne earlier said there was an international network "without which these attacks could not have succeeded".

Sri Lanka’s defence secretary earlier told the BBC that the country’s government and intelligence services should not be blamed for failing to prevent the Easter Sunday bombings.

Speaking at one of the bombed churches, St Anthony’s Shrine in Colombo, Hemasari Fernando said that information received earlier this month was of only one or two possible attacks, and that he never expected anything of this scale.

Mr Fernando - who is also chief-of-staff to the president - wouldn’t say if the country should brace itself for more attacks and refused to be drawn on whether all perpetrators had been arrested.

He said the bombings were an “unfortunate event” and the authorities were doing their best to protect the public, who should remain calm and peaceful.

Sri Lanka's National Security Council has announced plans to impose a "conditional state of emergency" from midnight.

A press release from the president's media unit referred to articles on combating terrorism as basis for the action.

It said the measures would target terrorism and would not limit freedom of expression.

It comes ahead of a national day of mourning scheduled for Tuesday for the 290 people killed in the attacks.

Authorities in Sri Lanka received warnings about a possible attack two weeks before the Easter Sunday assaults, cabinet spokesman Rajitha Senaratne has confirmed.

“On 4 April, 14 days before these incidents occurred, we had been informed about these incidents,” he said.

“On 9 April, the chief of national intelligence wrote a letter and in this letter many of the names of the members of the terrorist organisation were written down."

He said Prime Minister Ranil Wickremesinghe was not informed.

The BBC's Azzam Ameen in Colombo tweets:

Sunday's attacks were carried out with the help of an international network, a top Sri Lankan minister has said.

"We do not believe these attacks were carried out by a group of people who were confined to this country," cabinet spokesman Rajitha Senaratne said.

"There was an international network without which these attacks could not have succeeded."

Eyewitnesses of the bombing of Sri Lanka's St Anthony's Shrine have described horrific scenes.

Four staff members serving breakfast at a restaurant, the children of a billionaire and a woman who had just checked out of her hotel.

These are just some of the many victims the Sri Lanka attacks have claimed. Here's more on who they are.

Image source, Getty Images

Families of those killed in Sunday's attacks will receive compensation from the government.

In a press conference on Monday, cabinet spokesman Rajitha Senaratne said 100,000 Sri Lankan Rupees (£441;$573) would be paid towards funeral expenses and one million rupees as compensation for the families of everyone who died.

Those who suffered injuries would receive between 100,000 rupees and 300,000 rupees depending on the extent of their injuries.

All the damaged churches would be "completely repaired and renovated by the government", he added.

Eight Britons are now believed to be among the 290 people killed in Sunday's attacks, the BBC has been told.

Sri Lanka's foreign ministry had previously said five Britons, two with dual US citizenship, were among the dead.

But this morning Manisha Gunasekera, Sri Lanka's High Commissioner to the UK, has told Radio 4's Today programme: "As of now I think there's information on eight [British] nationals who have lost their lives."

• Read more: Eight Britons killed in explosions

Police have dismissed a rumour spreading online that poison had been mixed into the water supply in Kelaniya, Kiribathgoda and Ja-Ela, saying it is completely false.

The BBC's Azzam Ammeen tweets:

Venerable Prof Pitigala Vijitha Thero was outside St Anthony's Shrine in Colombo. He told the BBC he was "extremely saddened and grieved".

"Since the war, people belonging to all religions and faiths had been co-existing and living together in unity and harmony. This is not something that anyone could have anticipated."

He said he condemned the attacks, but "we don’t have any anger or ill will towards anyone of any other religion".

"I pray that peace prevails - not only in this country, but in the whole world," he added.

Nirj Deva, a British Member of the European Parliament (MEP), has told the BBC he narrowly missed the attack at the Kingsbury hotel, where he is a director.

Speaking to BBC Radio 5 Live, he said: "Had I arrived earlier as scheduled I would have been part of that carnage.

"They had used disgusting, barbaric bombs so lots of people had suffered very serious injury.

"It's been dreadful, disgusting, absolutely unspeakable acts of violence against innocent people.

"Why this island, which has gone through its own problems the last 40 years and just found itself peaceful and reconciling itself?"

A curfew will be imposed from 20:00 on Monday to 04:00 on Tuesday as a precautionary measure, the government announces.

These people have gathered outside the St Anthony's church in Kochchikade, Colombo. They have the terrible task of looking through images of the victims, taken at the police mortuary, to try to identify loved ones.

Image source, Reuters

The Associated Press has spoken to a Sri Lankan government forensic crime analyst, external, Ariyananda Welianga, who says analysis from the scene of the hotel and church attacks show they were carried out by suicide bombers. The investigators have been studying retrieved body parts.

The six attacks, he says, were perpetrated by seven attackers.

The two other explosions are still being investigated.

Three of the children of Danish billionaire Anders Holch Povlsen died in the attacks, a spokesman has confirmed to the BBC.

They were visiting Sri Lanka for the Easter holiday. The names and ages are not yet public.

Mr Povlsen, 46, owns the Bestseller clothing chain and is clothing giant Asos's largest shareholder.

Security officials drive past the Kingsbury, one of three luxury hotels targeted, with its blown-out windows still lying on the street.

Image source, EPA