Sri Lankan police have raided the headquarters of a hardline Islamist group founded by the suspected ringleader behind the Easter suicide bombings of churches and hotels. It comes as a ban on face coverings is due to come into force on Monday.

Armed police in the town of Kattankudy searched the headquarters of the National Thawheed Jammath (NTJ) and detained one man at the premises, a Reuters reporter at the scene said. Police did not comment.

On Saturday the government banned the NTJ under new emergency laws. The authorities believe the group’s founder, Zahran Hashim, masterminded the Easter Sunday attacks and was one of the nine suicide bombers who killed at least 250 people. Islamic State claimed responsibility for the attacks.

Police suspect the bombings were carried out by two local Islamist groups, including the one established by Zahran. Around 10,000 soldiers have been deployed around the island as the authorities hunt for more suspects.

The authorities have named the other group suspected of involvement as Jammiyathul Millathu Ibrahim.

Police sources told Reuters on Sunday that Zahran’s father and two brothers had been killed two days earlier in a gun battle with security forces. A relative identified the three men in a video circulating on social media calling for war against non-Muslims.

On Monday the ban on any face coverings in public comes into place. On Sunday, President Sirisena said he was using emergency powers to bring in the ban “to ensure national security”.

Only a small number of women in Sri Lanka wear the face-covering niqab.

The archbishop of Colombo, Cardinal Malcolm Ranjith looks on during a candle light vigil in memory of the victims on Sunday. Photograph: Lakruwan Wanniarachchi/AFP/Getty Images

On Sunday the archbishop of Colombo Malcolm Ranjith, who had asked churches to suspend Sunday mass due to security fears, delivered a televised special sermon from a chapel at his home. The service was attended by President Maithripala Sirisena, Prime Minister Ranil Wickremesinghe and former president Mahinda Rajapaksa.

The vast majority of those killed in the Easter Sunday attacks were Sri Lankans. The dead also included 40 foreigners, including British, American, Australian, Turkish, Indian, Chinese, Danish, Dutch and Portuguese nationals.

Mourners light candles during a vigil in memory of the bomb blast victims in Colombo. Photograph: Jewel Samad/AFP/Getty Images

Police believe that radical Muslim preacher Zahran led the NTJ - or a splinter faction - to mount the attacks in Colombo as well as on a church in Batticaloa in the east. The authorities have named the other group suspected of involvement as Jammiyathul Millathu Ibrahim.

More than 100 people, including foreigners from Syria and Egypt, have been detained for questioning for questioning over the Easter attacks.

The Sri Lankan military said at least 15 people were killed during a fierce gun battle with Islamist militants on the east coast on Friday, including six children.

In an apparent reference to the three men, Islamic State said on Sunday that three of its members had clashed with Sri Lankan police for several hours on Friday before detonating their explosive vests. It did not name them.