Sri Lankan police have detained a Syrian among 40 people who are being questioned about the Easter Sunday attacks on churches and hotels, Hindustan Times reported quoting government and military sources.

No group has claimed responsibility for the attacks, which officials said were carried out by at least seven suicide bombers on three churches and three hotels.

However, the focus of suspicion is falling on Islamist militants with links to foreign groups. US intelligence sources said the attacks bore some of the hallmarks of the Islamic State extremist group.

Tuesday was declared a national day of mourning and the funerals of some of the victims were held as pressure mounted on the government over why effective action had not been taken in response to a warning this month about a possible attack on churches by a little-known domestic Islamist group.

Police said the number of people arrested since Sunday had risen to 40, most of them Sri Lankans.

“The investigation of those detainees led to the Syrian. He was arrested after the interrogation of local suspects,” sources told Reuters.

Most of the dead and wounded were Sri Lankans, although government officials said 38 foreigners were killed. That included British, U.S., Australian, Turkish, Indian, Chinese, Danish, Dutch and Portuguese nationals.