Sri Lanka suicide bomber FAMILY: Two brothers blew themselves up in terror attack, then wife of one killed herself and their two children with explosives when police raided their home

Two sons of a wealthy spice trader carried out suicide blasts in the Sri Lanka terror attacks on Easter Sunday, it has been claimed.

The Muslim brothers, whose names have not been revealed, blew themselves up as guests queued for breakfast at the Shangri-La and Cinnamon Grand hotels in the capital.

They were in their late twenties and operated their own 'family cell', an investigation officer said as Sri Lankan police continue to probe the bombings that killed 321 people. It is not known where their parents are.

One brother gave false identity details when he checked into the hotel, but the other gave a real address which led police commandos to their family home in a commercial area of Colombo.

When the Special Task Force went to the house to investigate, one brother's wife set off a bomb, killing herself and her two children, according to police sources.

Three police commandos were killed in the blast, and several extended family members are among those in detention.

'It was a single terror cell operated by one family,' the investigator said. 'They had the cash and the motivation. They operated the cell and it is believed they influenced their extended family.'

'What we have gathered so far is that they had indicated to their close family what they were going to do,' another senior police officer said.

'It looks like they were inspired by foreign terrorist groups, but to what extent they had direct links is still unclear.'

The brothers had been involved in their father's lucrative Colombo spice export business, investigators said.

A focus of the inquiry will be to find out whether there was a foreign influence in their radicalisation and how the children of such a wealthy family had become involved, an official source said.

The pair were key members of the Islamist National Thowheeth Jama'ath (NTJ) group, the official added.

ISIS has claimed responsibility for the attacks, but the government has blamed the NTJ.

A minister said Tuesday the bombers may have struck in revenge for attacks on two New Zealand mosques last month which left 50 dead.

Investigators said it was not known whether the brothers were in contact with the other bombers.

The first wave of attacks struck during busy Easter services at churches in the cities of Colombo, Negombo and Batticaloa.

More bombs ripped through three luxury hotels in the capital city of Colombo: the Kingsbury, the Shangri La, and the Cinnamon Grand.

The group also planned another attack at a fourth hotel, but the suicide bomber either failed to detonate his device or decided against doing so, official sources said.

After the Shangri-la blast, staff at the unnamed hotel the would-be attacker checked into became suspicious and reported him to police.

The man was tracked to a lodging near the capital, where he blew himself up when confronted by police, killing two bystanders.

'What we have seen from the CCTV footage is that all the suicide bombers were carrying very heavy backpacks. These appear to be crude devices made locally,' the source said.

Police are also currently on the hunt for a van and a lorry that are believed to be carrying explosives, reports News 1st. They are also on the look out for three motorbikes, a cab and a van.

With 321 people confirmed dead, including at least 39 foreign nationals, and over 500 wounded, Sri Lanka has declared a state of emergency and launched a desperate hunt to head off more attacks.