Who are National Thowfeek Jamaath and what does the Sri Lanka attack tell us about their relationship with ISIS?
As authorities try to establish the events leading up to the explosions which killed 310 people in bombings across Sri Lanka, more information about the terror group which carried out the deadly attacks has being revealed.
National Thowfeek Jamaath has been named as the group responsible, but according to US security experts, the Islamist group had help from ISIS.
Sri Lankan health minister Rajitha Senaratne said: "We do not believe these attacks were carried out by a group of people who were confined to this country.
“There was an international network without which these attacks could not have succeeded.”
On Tuesday, Islamic State said it carried out the attack - but what does its claimed possible link-up with a smaller group tell us about how the fight against terror might be changing?
ITV News Security Editor Rohit Kachroo said National Thowfeek Jamaath "certainly weren't a household name" but they were "more than familiar to Sri Lankan authorities and their counterparts around the world".
All the bombers were Sri Lankans, but Kachroo believes the level of scale and coordination of the attacks suggests National Thowfeek Jamaath - which has no history of major attacks - had help from groups outside of Sri Lanka.
Regarding indicators of what made the attack an international affair, he said: "Consider the mechanics of not only the devices that did go off, but that ones that didn't."
"Colombo bus station last night, 87 detonators were discovered. Colombo airport, a six foot pipe bomb packed with 50kg of explosives.
"These were a huge amount of explosives, and of course a large operation involving people so extreme, so radicalised that they were willing to blow themselves up.
"Sri Lanka has a fairly sophisticated counter-terrorism structure, it grew out of the civil war there, it might be very worrying if they failed to spot it right under their noses if this was a domestic terror plot...
"Perhaps more worrying would be if this was part of an international network that somehow global organisations like al-Qaeda or ISIS had contracted this out to a local organisation and this might be a sign of where the global fight against terror goes from now on."