Easily-available chemicals used for bombs: Sri Lankan PM

Wickremesinghe said the investigating authorities have been tracking the trail of explosives used to manufacture the bombs detonated on April 21 to target churches and luxury hotels on the island.

"We have been tracking the arms. Many of them are chemicals that they have used. Some of the chemicals were available, some of it you could easily purchase. For instance, they have found a large number of ball bearings. Over a long period of time, you can purchase them," he was quoted as saying by Efe news on Monday.

The Prime Minister noted that there was now a "question of funding and where the know-how to put these together" came from.

"These are explosives which had to be kept in a certain climate and certain temperatures," he said.

Wickremesinghe was speaking days after the Easter Sunday suicide bombings killed 253 people in the country, which has been in a state of Emergency since the attacks claimed by Islamic State terror group.

The government has deployed thousands of troops to round up any remaining suspected Islamist extremists on the island nation, where Christians make up 7.4 per cent of the population, with Buddhists accounting for 70.2 per cent, Hindus 12.6 per cent and Muslims 9.7 per cent.

Wickremesinghe said the group of militants behind the attacks might have "self-funded" their activities as they were from affluent families.

However, it is believed that intelligence officials are also tracking financial records to see if foreign organizations helped the bombers with funds to carry out the attacks.

The Si Lankan government has been heavily criticized for its apparent failure to prevent the worst carnage the country has suffered since the 26-year-old civil war between Tamil guerrillas and government ended in 2009.

President Maithripala Sirisena last week blamed intelligence failures for the devastating bombings amid reports that there were prior warnings that Islamist extremists were planning attacks.

Wickremesinghe said that the series of well-coordinated explosions could have been prevented "if security agencies followed instructions given to them".

He said the attacks were carried out by a "well knit... small group of people".

The authorities, he claimed, were aware of the group but didn't know that they had transformed from "extremism to violence".

He said the group recruited its members from within inner circles, canvassing with "a friend or a brother to come in" or recruiting "their wives".

Sri Lankan intelligence agencies also confirmed that the group initially used messaging app Telegram to communicate and propagate Islamic State ideologies but later moved out of it to escape being detected.

Wickremesinghe said many from the group were in Colombo and used to meet "each other and had their own (means of) communications".

The security agencies have been trailing some families linked to obscure local extremist groups - National Thowheed Jamath and Jammiyathul Millathu Ibrahim - since the attacks and apprehended nearly 160 people.

At least 17 people, six of them minors, died during a police crackdown on Saturday against an armed group suspected of having a hand in the Easter attacks.

The dead included father and brothers of the suspected ringleader of the Easter Sunday bombings, Mohamed Zahran Hashim. He is said to have died in a suicide blast in Hotel Shangri-La of Colombo.

His wife and daughter, who sustained injuries during the Saturday crackdown, have been placed under police custody.

Wickremesinghe said that the government would introduce new laws to regulate and monitor Muslim religious schools as they have done with Buddhist schools.

This comes in the wake of the revelation that Islamic State doctrine had infiltrated the country's moderate Muslim society, targeting affluent businessmen and professionals from the upper-middle class.

Wickremesinghe refused to discuss the effect the attacks would have on his political career amid speculation that he will be running for the President's office in the election set for later this year.