SINGAPORE - A delivery man who robbed a prostitute at knifepoint and made her perform oral sex on him was jailed for 3 1/2 years and ordered to be given 12 strokes of the cane on Wednesday.

Koh Meng Yeow, 32, who pleaded guilty, robbed the 24-year-old Vietnamese national of her $900 mobile phone, $400 cash, one Special Pass and her identity card while armed with a penknife near Changi Coast Road on Sept 11.

A district court heard that Koh went to Lorong 16 Geylang for dinner at about 9pm the previous night. He then wandered around the area and thought of his financial problems before deciding to rob someone.

While driving the company lorry around at about 1am, he spotted the victim standing at Lorong 30 Geylang. He wound down his window and asked "how much?", then nodded his head when she informed him it was $80 for an hour.

He told her to get into the lorry. She directed him to a hotel at Lorong 34 Geylang - but instead of heading there, he kept on driving.

At one point, the victim asked him to take her back to Geylang but he remained silent, Deputy Public Prosecutor Elaine Liew said.

Later, he stopped his vehicle at a deserted area near Changi Coast Road. He took out a penknife from the front glove compartment and held it near her neck. She began to cry.

He took her handbag and robbed her of her belongings - before telling her to undress and perform the sex act on him.

Subsequently, he took out $20 from her handbag, gave it to her and asked her to get out before driving off.

A third charge of posing as a cop was considered during his sentencing.

Koh, who has a previous conviction for drug consumption, could have been jailed for up to 14 years and caned at least 12 times for armed robbery. The maximum penalty for the sex offence is 20 years, fine and caning.