It is "heartbreaking" to see his two sons go to jail for evasion of national service obligations, but Senior Counsel Tan Chee Meng says he is taking responsibility for what happened and letting the law take its course.

In a statement issued after his younger son was sentenced yesterday, Mr Tan said the decision by him and his wife to uproot the family and migrate to Canada in 2000 was made in their sons' best interest.

The court had heard earlier that the sons were unable to cope with the Singapore education system's policy of having a compulsory mother tongue language to study and that the younger one suffered a form of eczema that is worsened by the hot and humid weather here.

"NS was the last thing on our minds, let alone evasion. It was not an easy decision," added Mr Tan, who is deputy chairman of WongPartnership law firm.

But he said his sons later decided on their own in 2015 that they wanted to serve NS, a decision that the father said he is "very proud of".

The decision led to both sons - Jonathan Tan Huai En, 28, and Isaac Tan Yang En, 25 - being convicted and jailed for NS evasion.

The younger son was sentenced yesterday to 12 weeks' jail for evading NS for about six years, while the elder was sentenced to 16 weeks' jail in February for a similar offence involving a 10-year default period.

"As a father, it is heartbreaking to see my sons go to jail in circumstances such as these. I take responsibility for what happened and the law has to take its course.

"The past 21/2 years have not been easy but we will get through this as a family," said Mr Tan.

Isaac Tan, who is now serving his NS and will complete it later this month, pleaded guilty last Friday to one count of remaining outside Singapore without a valid exit permit. A second charge for a similar offence and one count of failing to comply with a Further Reporting Order to report for NS registration, pre-enlistment documentation and medical screening were taken into consideration during sentencing.

Brother Jonathan Tan surrendered himself last week to begin his jail term after withdrawing an appeal against his sentence.

On Dec 1, 2000, Isaac Tan migrated to Canada with his mother, older sister and brother. He returned to Singapore in August 2015 after completing his university studies in Canada, and began full-time NS two months later.

District Judge Marvin Bay said yesterday Isaac Tan had shown "no evident urgency" despite being told in October 2014 that he was classified as an NS defaulter and had to return to Singapore to respond to the offences and fulfil his NS duty.

Judge Bay said NS is a critical obligation and cannot be relegated to a task to be performed at a time of one's own convenience. He added that punishment must aim at deterring potential offenders from gaming the system or thinking that the reward for postponing their NS obligations can outweigh the costs of the legal punishment.

In July, a High Court panel led by Chief Justice Sundaresh Menon set a new sentencing framework for NS defaulters, comprising four bands based on the default period.

For periods of two to six years, the starting point is two to four months in jail; for seven to 10 years, it is five to eight months in jail; and for 11 to 16 years, it is 14 to 22 months in jail.

For the worst cases lasting 17 to 23 years or more, the default jail term starts from two years to the maximum of three years in jail.