The pregnant wife of a Sri Lankan suicide bomber has detonated a suicide vest killing her self, her children, and police officers.

The wife of the suspected mastermind behind the Easter Sunday bombings detonated the explosives as police raided the family's Colombo home, Sri Lanka's Deputy Defence Minister Ruwan Wijewardene said.

At the centre of the plot that has devastated the peaceful Southeast Asian nation are two brothers, according to reports. They were the sons of a rich spice merchant, and they lived in one of the most lavish mansions in their wealthy suburb in Colombo.

The mastermind of the suicide bomb plot is now believed to have been Inshaf Ibrahim, in his 30s, who owned a copper factory. He is said to have detonated his own explosive device at the Shangri-La hotel, by the busy breakfast buffet, a source close to the family told reporters.

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When the lavish and sprawling Ibrahim home was raided shortly afterwards, the pregnant wife of one of the brothers was in the home wearing a suicide vest, Mr Wijewardene said according to the ABC.

As police arrived, the woman reportedly detonated the vest, killing herself, her two children and three police officers, news.com.au reports.

Ilham Ibrahim had expressed extremist views and been involved in meetings with local group Tawheed Jamaath, a Islamist group suspected of involvement and planning of the bombings.

His brother, Inshaf, was publicly known to be more moderate in his views. Married to the daughter of a wealthy jewellery manufacturer, he had given donations to local struggling families.

Their father Mohamed Ibrahim, a wealthy spice trader, admired pillar of the community, and father of nine, has been arrested in the wake of the attacks.

Most of the suicide bombers were from educated, wealthy families, according to Mr Wijewardene. Some had law degrees and all were Sri Lankan, he added.

"That's a worrying factor in this because some of them have studied in various other countries," he said.

"They hold degrees. We believe one of the suicide bombers studied in the UK and later on did his postgraduate in Australia before coming back to Sri Lanka."

Speaking in Townsville, Australian Prime Minister Scott Morrison confirmed one of the attackers had spent time living in Australia.

"I can confirm the suicide bomber had been in Australia," Mr Morrison said.

"They departed in early 2013. That individual had been here on a student and graduate skilled visa. They had no visa (since)."

A woman holds a crying child as she throws earth onto a coffin during a funeral for a person killed in the Easter Sunday attack on St Sebastian's Church. Photo / Getty Images
A woman holds a crying child as she throws earth onto a coffin during a funeral for a person killed in the Easter Sunday attack on St Sebastian's Church. Photo / Getty Images

The man had also held a spouse and child visa at a time. After leaving in 2013, they didn't return to Australia.

"It's a matter of an ongoing investigation so I wouldn't say anything other than what (I have)."

SRI LANKA SHAKES UP TOP SECURITY POSTS AFTER DEADLY BOMBINGS

Sri Lanka's president shook up the country's top security establishment after officials failed to act on intelligence reports warning of possible attacks before the Easter bombings that killed over 350 people, his office said on Wednesday.

The capital of Colombo, meanwhile, remained rattled by reports police were continuing to conduct controlled detonations of suspicious items three days after the attacks on churches and luxury hotels, and the US ambassador said Washington believed "the terrorist plotting is ongoing".

During a televised speech to the nation on Tuesday night, President Maithripala Sirisena said he would change the head of the defence forces within 24 hours, and on Wednesday he asked for the resignations of the Defence Secretary and national police chief in a dramatic internal shake-up. He did not say who would replace them.

Mr Sirisena said he had been kept in the dark on the intelligence about the planned attacks and vowed to "take stern action" against officials who failed to share it.

Government leaders have acknowledged some intelligence units were aware of possible attacks weeks before the bombings that struck three churches and three luxury hotels. The death toll rose on Wednesday to 359, with 500 people wounded.

Police spokesman Ruwan Gunasekara also said 18 suspects were arrested overnight, raising the total detained to 58.

Sri Lankan authorities have blamed a local extremist group, National Thowheed Jamaat, whose leader, named Mohammed Zahran or Zahran Hashmi, became known to Muslim leaders three years ago for his incendiary online speeches.

Yesterday, Mr Wijewardene said the attackers had broken away from National Thowheed Jamaat and another group, which he identified only as "JMI". Islamic State has claimed responsibility for the attacks.

Security personnel stand guard at St Anthony's Church on April 24, 2019 in Colombo, Sri Lanka. Photo / Getty Images
Security personnel stand guard at St Anthony's Church on April 24, 2019 in Colombo, Sri Lanka. Photo / Getty Images

Authorities remain unsure of the group's involvement, though are investigating whether foreign militants advised, funded or guided the local bombers.

Mr Wijewardene said many of the suicide bombers were highly educated and came from well-to-do families.

"Their thinking is that Islam can be the only religion in this country," he told reporters.

A British security official confirmed a report a suicide bomber who is believed to have studied in the UK between 2006 and 2007 was Abdul Lathief Jameel Mohamed.

The security official, who spoke on condition of anonymity because of the sensitive nature of the investigation, said British intelligence was not watching Mohamed during his stay in the country. His name was first reported by Sky News.

A team of FBI agents and US military officials were helping in the investigation, US Ambassador Alaina Teplitz said.

She told reporters "clearly there was some failure in the system" and the US had no prior knowledge of a threat before the attacks, the worst violence in the South Asian island nation since its civil war ended a decade ago.

Ms Teplitz called that breakdown in communication among Sri Lankan officials "incredibly tragic".

The US remained concerned over militants still at large and believed "the terrorist plotting is ongoing", Ms Teplitz said, adding Americans in Sri Lanka should continue to be careful.

Although no more bombs were found on Wednesday, Sri Lanka has been on heightened alert since the attacks, with police setting off a series of controlled explosions of suspicious objects. The military has been given sweeping police powers it last used during a devastating civil war that ended in 2009.

Government statements about the attacks have been confused and sometimes contradictory, with Mr Gunasekara telling reporters there were nine suicide bombers — two more than officials said one day earlier.

One of the additional bombers was the wife of another bomber, he said. The woman, two children and three policemen died in an explosion as authorities closed in on her late on Sunday, hours after the main attacks were launched.

NINTH BOMBER STILL NOT IDENTIFIED

The ninth suicide bomber has not been identified, though two more suspects were killed in a later explosion on the outskirts of Colombo.

Prime Minister Ranil Wickremesinghe has edged away from comments made by his state minister of defence that the bombings were carried out in apparent retaliation for the March 15 mosque shootings in Christchurch, New Zealand that killed 50 people.

He told reporters on Wednesday the mosque attack may have been a motivation for the bombings, but there was no direct evidence of that.

An Australian white supremacist was arrested in the Christchurch shootings. While Sri Lanka's recent history has been rife with ethnic and sectarian conflict, the Easter bombings still came as a shock to the country of 21 million people.

It is dominated by Sinhalese Buddhists but also has a significant Tamil minority, most of whom are Hindu, Muslim or Christian.

Tamil Tiger rebels were known for staging suicide bombings during their 26-year civil war for independence, but religion had little role in that fighting.

The Tigers were crushed by the government in 2009. Anti-Muslim bigotry, fed by Buddhist nationalists, has swept the country since the war ended, but Sri Lanka has no history of Islamic militancy. Its small Christian community has only experienced scattered incidents of harassment.