The archbishop of Colombo, Cardinal Malcolm Ranjith, said on Thursday (May 2) that a "reliable foreign source" had alerted him to possible attacks this weekend.
"The information we have from a reliable foreign source is that attackers are planning to hit a very famous church and a Catholic institution," the Cardinal said in a statement. He did not name the source.
He also said that Catholic schools which were due to reopen after an extended Easter vacation on Monday would now remain shut "until further notice".
Sri Lankan authorities had advance warnings from Indian intelligence of the impending Easter attacks in which 257 people died, but police and security forces ignored them.
'SEARCHED AND SAFE'
However, the government said all 10,194 public schools will reopen on Monday amid tight police and military security, with at least one armed guard outside each one.
"We have been assured that all schools will be searched and safe for us to resume the new school term," Education Minister Akila Kariyawasam told reporters in Colombo.
Last Sunday, a week after the April 21 attacks, all public masses were cancelled and Cardinal Ranjith conducted a private memorial service for the victims that was broadcast live on television.
Armed guards have been stationed outside churches, Buddhist temples and mosques across the country since the April 21 attacks on three churches and three luxury hotels.
All political parties scrapped May 1 rallies amid fears of bomb blasts.
The Cardinal has also been given several bodyguards and a large security contingent but returned a bullet-proof limousine given to him by the government.
"I am not afraid. I don't need bullet-proof vehicles to go about. The Lord is my protector," he said. "But I want security for my people, and for the country."
Ranjith said he had concerns about the progress of security operations against militants behind the worst single-day attack against civilians in the country's history.
Police say they have arrested more than 150 suspects since the attacks and have accounted for all six suspects who were declared as most-wanted.
Two suspects have been killed while four others were in custody, police said.
President Maithripala Sirisena announced on Friday that the authorities believed there were 140 Islamic State in Iraq and Syria (ISIS)-inspired militants in Sri Lanka and he had ordered security forces to track them down.
The Easter attacks were blamed on the local National Thowheeth Jama'ath (NTJ) whose leader was among the suicide bombers. The group had pledged an oath of allegiance to ISIS.
Meanwhile, police said Muslim clerics had refused to preform burial rites for 10 Muslim radicals who were killed during a confrontation with security forces in the island's east last week.
Three suicide bombers killed themselves and three women and six children inside an Islamist safe house near the town of Kalmunai. Another four people defending the house were shot dead by security forces.
"No relatives or clerics agreed to perform the final rites, so the police took steps to bury them," spokesman Ruwan Gunasekera said.
The six children were spared that fate, he added.
Clerics have previously said they would not undertake last rites for any of the suicide bombers involved in the attacks.