Sri Lanka's Catholic church suspended all public services over security fears on Thursday, as thousands of troops joined the hunt for suspects in deadly Easter bombings that killed nearly 360 people.

Authorities made fresh arrests and stepped up security measures as the government faced pressure over its failure to act on Indian intelligence warnings before the suicide bombers blew themselves up in luxury hotels and churches packed with Easter Sunday worshippers.

A senior Catholic priest told AFP that all public services were being suspended and all churches closed "on the advice of security forces".

Private burials will still be carried out.

Security forces using state of emergency powers arrested 16 more suspects overnight, bringing the total in custody to 74 since the attacks.

Brigadier Sumith Atapattu said the army had increased its deployment on the streets from 5,000 to 6,300, with the navy and air force also deploying an additional 2,000 personnel.

- 'Major' lapse -

The government has been on the defensive over revelations that warnings about an attack went ignored.

Sri Lanka's police chief warned on April 11 of possible suicide bombings against churches by local Islamist group National Thowheeth Jama'ath (NTJ), citing information from a foreign intelligence agency.

India warned Sri Lanka several times of possible attacks, based on information from suspects arrested in India over links to the Islamic State group, a source close to the Indian investigation told AFP.

But that information was not shared with top ministers in Sri Lanka, the Colombo government has conceded.

"It was a major lapse in the sharing of information," deputy defence minister Ruwan Wijewardene said Wednesday.

President Maithripala Sirisena, who is also defence and law and order minister, has pledged to make "major changes in the leadership of the security forces.

He has asked the police chief and top defence ministry bureaucrat to step down, though neither has done so yet.

On Thursday, Sirisena met political and religious figures to discuss the crisis, amid concerns about a potential backlash against Sri Lanka's Muslim minority.

Investigators are still piecing information together about the attacks and those involved. Wijewardene revealed Wednesday that one attacker had studied in Britain and did post-graduate studies in Australia before returning to Sri Lanka.

He said most were "well-educated and come from middle, upper-middle class families, so they are financially quite independent."

- Key suspect -

Experts say the bombings had many of the hallmarks of the Islamic State group, which has claimed responsibility for the attacks. The government has indicated it believes the local militants had outside help.

An FBI team is now in Sri Lanka and Britain, Australia and the United Arab Emirates have also offered intelligence help.

A key suspect in the attacks still remains unaccounted for: NTJ leader Zahran Hashim.

He appears to be among eight people seen in a video released Tuesday by IS after it claimed the attacks.

Officials said it was still unclear whether Hashim was among the suicide attackers or had escaped.

Authorities have said they cannot rule out further attacks while suspects are at large.

Tensions remain high, with many of the capital's road deserted Thursday as rumours circulated about new bombs. Police investigated several suspicious packages, but said none contained explosives.

In Batticaloa in eastern Sri Lanka, where a church was targeted in the attacks, security was also heavy.

"We are working around the clock now, 21 hours a day, because of what happened," said one police officer manning a checkpoint in the baking heat.

In all, nine people are believed to have blown themselves up on Sunday, either during attacks or when police attempted to arrest them.

Sri Lankan police sources have told AFP that two Muslim brothers, sons of a wealthy Colombo spice trader, blew themselves up at the Shangri-La and the Cinnamon Grand hotels.

Their father is now in custody.

The Kingsbury hotel in the capital was the last one hit, along with three churches. A fourth planned attack on a hotel failed, authorities said. The would-be attacker was followed back to a Colombo guest house, where he blew himself up, killing two people.

Two more people -- a man and a woman -- blew themselves up at another location as security forces launched a raid, killing three police, sources said.

Dozens of foreigners were among the victims of the blasts, including eight Britons, 10 Indians and four Americans.

The United Nations said at least 45 children, Sri Lankans and foreigners, were among the dead.