Sri Lanka's police Saturday arrested a top Muslim leader and member of parliament in connection with the 2019 Easter Sunday attacks that killed 279 people as pressure to speed up the investigation mounted.

Detectives took Rishad Bathiudeen, leader of the All Ceylon Makkal Party, into custody under the Prevention of Terrorism Act (PTA), police spokesman Ajith Rohana said.

He said Bathiudeen and his brother Riyaaj were arrested in pre-dawn raids on their homes in Colombo.  

"They were arrested under the PTA based on circumstantial and scientific evidence that they had connections with the suicide bombers who carried out the attacks," Rohana said in a statement.

The arrests came three days after the head of Sri Lanka's Roman Catholic Church, Cardinal Malcolm, accused the government of allowing investigations to stall.

Nearly 200 people were arrested within days of the suicide attacks on hotels and churches by local Islamist extremists, but no one has yet been charged.

Ranjith, who led commemorations on the second anniversary of the Easter attacks on Wednesday, said he was "deeply saddened" by the lack of progress in the investigation.

He renewed his call for swift action against the perpetrators and said "political posturing and the need to safeguard alliances" was hindering the probe.

MPs from Bathiudeen's party had provided crucial support to President Gotabaya Rajapaksa in October to amend the constitution and give him wider powers over the judiciary and the legislature.