President Maithripala Sirisena speaks during a meeting. File

Allowed to detain and interrogate suspects without court orders, Sri Lanka's police and military have arrested more than 100 suspects in the crackdown after the hardliner militant attacks.

President Maithripala Sirisena issued orders for the law to be extended for another month from midnight on Friday, according to a gazette notification seen by media.

Authorities say the threat of more attacks has been contained and security services have dismantled most of the network linked to the bombings, but operations were still underway to find any remaining suspects.

Sirisena said in the notification that extending emergency rule was "in the interest of public security, the preservation of public order and the maintenance of supplies and services essential to the life of the community."

The attacks sent shockwaves through the Indian Ocean island state, which had enjoyed relative peace since a civil war ended a decade ago.

The economy has slowed worryingly, forcing the government to seek foreign loans, and the lucrative tourism industry has been hit.

Despite three advance intelligence reports from India that attacks were being planned, Sri Lanka's top defence officials failed to act before the Easter Day suicide bombings by hardliner militants that targeted three churches and three luxury hotels.

Daesh claimed responsibility for the attacks that killed more than 250 people, including 42 foreigners, though Sri Lankan authorities have blamed two little known domestic groups: the National Thawheedh Jamaath (NTJ) and Jamathei Millathu Ibrahim.

Both have been banned under the emergency regulations.

Sirisena told foreign diplomats in May that he planned to lift the emergency once the security situation was "99 per cent" back to normal.

Reuters