Car, bomb scare rattle nervous Sri Lanka

Sri Lankans continue to mourn as police round up people for questioning over deadly terror attacks. (AAP)

Sri Lankan authorities briefly locked down the central bank and shut the road leading to Colombo airport amid a jittery atmosphere after the Easter bombings.

Sri Lankan authorities locked down the central bank and briefly shut the road leading to Colombo airport on Thursday as more people were swept up in the search for those behind Easter Sunday bombings that killed 359.

Two bank officials told Reuters the street outside the building near the World Trade Centre in the capital was blocked before the security alert was lifted.

Underscoring the nervous atmosphere in the Indian Ocean nation, authorities also shut the entry road to Colombo's main airport after a suspicious vehicle was identified at a nearby car park, which proved a false alarm.

A police spokesman also said there was an unexplained explosion in a town east of the capital, but there were no casualties.

More people, including foreigners, were swept up for questioning overnight as authorities probed deeper into the bombings, which were potentially the deadliest operation claimed by Islamic State.

Police said an Egyptian and several Pakistanis were among those detained, although there was no immediate suggestion they had direct links to the attacks.

Police on Thursday detained 16 more people for questioning overnight, taking the number detained since Sunday to at least 76.

A picture has slowly emerged of a group of nine well-educated, home-grown Islamist suicide bombers, including a woman, who carried out the attacks.

However, Sri Lankan and international authorities have also focused investigations on international links to domestic Islamist groups National Thawheed Jama'ut and Jammiyathul Millathu Ibrahim.

Islamic State claimed responsibility for the attacks but offered no firm information to back up its claim.

The Islamist group released a video on Tuesday that showed eight men, all but one with their faces covered, standing under an Islamic State flag and declaring their loyalty to leader Abu Bakr Al-Baghdadi.

The one man in the video with his face uncovered has been identified as Mohamed Zahran, a preacher from the east of Sri Lanka known for his militant views who may have been the attack's mastermind.

Australian Prime Minister Scott Morrison said another of the bombers had lived in Australia with his wife and child on a student visa but left the country in 2013.

Morrison did not identify the man, although his family have said his name was Abdul Latheef Mohamed Jameel.

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

Police also said they detained an Egyptian who was found not to have a valid visa or passport. The man taught Arabic in a school about 70km from the capital and had been in Sri Lanka for more than seven years.

A police spokesman also said a group of Pakistanis had been detained for overstaying their visas.

The bombings shattered the relative calm that has existed in Buddhist-majority Sri Lanka since a civil war against mostly Hindu, ethnic Tamil separatists ended 10 years ago, and raised fears of a return to sectarian violence.

President Maithripala Sirisena will meet representatives of different faiths later on Thursday to address concerns of a sectarian backlash.

Sri Lankan officials have said they believed the bombings were carried out in retaliation for the March 15 attacks by a lone gunman on two mosques in New Zealand that killed 50 people.

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