An elderly Sri Lankan woman cries sitting next to the grave of her family member who died in Easter Sunday church explosion in Sri Lanka. Picture: AP Photo/Eranga Jayawardena

Colombo - Five days after coordinated bombings on Easter Sunday left more than 350 people dead, this shellshocked tropical nation and its capital remained on edge Thursday, as officials warned of new possible attacks and religious leaders canceled services around the country.

The national police inspector general's office circulated a letter Thursday to other police agencies, saying that the same groups that carried out the Easter attacks had threatened to attack mosques where Muslim religious leaders were buried. The letter, a copy of which was obtained by The Washington Post, said the threat should be taken seriously and addressed with urgent measures.

Sri Lankan Prime Minister Ranil Wickremesinghe, in an interview with the Associated Press, warned that suspects linked to Sunday's attacks remain at large and "may go out for a suicide attack."

The U.S. Embassy in Colombo in a tweet urged people to avoid places of worship because of the risk of additional attacks.

Fallout over government failures to act on warnings of possible terrorist attacks around Easter prompted defense secretary Hemasiri Fernando, whose resignation was demanded by Sri Lanka's president Wednesday, to step down from his post. His departure was the second high-level official change stemming from the bombings.

The national police inspector general, Pujith Jayasundara, resigned Wednesday.

Security forces in Colombo, the capital, cordoned off and searched the country's Central Bank and several office buildings. They also searched the luxurious suburban home of a wealthy Muslim spice trader whose two sons were among the suicide bombers.

Police officials and a former navy chief told media outlets Thursday that the merchant, a prominent business leader named Y.M. Ibrahim, had been arrested on charges of aiding his sons in the attacks.

The road to the national airport, about 20 miles from the capital, was briefly blocked while security squads searched a suspicious car, and aviation officials said they were banning the use of drones, which have been used by some militant groups to carry explosives. A small explosion was reported in another suburb, but no damage or injuries resulted.

Police in the capital arrested three people with grenades and swords, and employees at one luxury hotel attacked Sunday were told to remain indoors. As police continued to search for explosives, they detonated a suspicious item found in a garbage dump in Pugoda, a town 35 miles from Colombo.

Many shops and restaurants remained closed in Colombo, where a nighttime curfew remained in effect, and the nearby seaside city of Negombo, where the deadliest bombing took place. Church officials in Negombo have already conducted about 75 funerals and burials since Monday, but formal religious ceremonies there have now paused for security reasons. One church official there said he had been told that police were still searching for bombing suspects in the area.

The country's senior Muslim government official, M.H. Abdul Halim, issued an urgent written appeal Thursday asking all Muslims to "avoid gathering" for congregational prayers on Friday and instead to remain at home and "pray for the peace and security of the motherland."

Halim, the federal minister of postal services and Muslim affairs, said he was acting "in solidarity" with the Catholic church and "in protest against the barbaric acts" of the bombers.

Many Muslims have expressed fears of being blamed the bombings and targeted for attacks, and streets and shops in Muslim communities in both cities have been deserted and on edge. Some people said they were worried about security conditions during Ramadan, the Muslim month of fasting and prayer, which begins in several weeks.

"I can't go to work, I can't go to shop, I don't want to leave the neighborhood. I'm even afraid to go to the mosque," Mohammad Rahmatullah, 62, who runs a street paving company, said as he sat disconsolately outside his modest home on a dirt alley in Negombo on Wednesday.

The Washington Post