"The preliminary investigations have revealed that what happened in Sri Lanka (on Sunday) was in retaliation for the attack against Muslims in Christchurch," state minister of defence Ruwan Wijewardene told parliament.

Fifty people were killed in shooting attacks on two mosques in the New Zealand city of Christchurch on March 15.

Wijewardene said investigations showed that a local group called National Thowheeth Jama'ath (NTJ) was behind the attack and was linked to a little-known radical Islamist group in India.

"This National Thowheeth Jama'ath group which carried out the attacks had close links with JMI it has now been revealed," Wijewardene told parliament, in an apparent reference to a group known as Jamaat-ul-Mujahideen India.

Little is known about JMI, other than reports it was established last year and is affiliated to a similarly named group in Bangladesh.

The minister said Sri Lanka was receiving unspecified international assistance with the investigation.