SINGAPORE - President Halimah Yacob and Prime Minister Lee Hsien Loong wrote to Sri Lanka's leaders on Monday (April 22) to convey their condolences following a string of bombings at churches and high-end hotels in the Indian Ocean island a day ago.

Expressing her deep sadness over the attacks, President Halimah, in her condolence letter to her Sri Lankan counterpart Maithripala Sirisena, said such "senseless and indiscriminate acts of violence" against innocent civilians "can never be justified".

"On behalf of the people of Singapore, I convey my deepest condolences and sympathies to those who lost their loved ones in this tragedy. Our thoughts are with the government and people of Sri Lanka during this difficult time," she said.

In his letter to Prime Minister Ranil Wickremesinghe, PM Lee said Singapore condemned such senseless acts of violence against innocent civilians.

"That many of the victims were worshipping or spending the holiday weekend in your beautiful country makes this even more painful and shocking. We stand firmly behind Sri Lanka in its effort to preserve its hard-wrought peace and stability," he said.

"I am confident that under your leadership, Sri Lanka will remain united and find strength to overcome this grief and adversity."

Sunday's bombings killed 290 people and wounded about 500.

There was still no claim of responsibility for the blasts, and fears abound that more attacks are possible.