McDonald's has apologised for its "PSI" advertisement which some felt was tasteless when it was published in The Straits Times yesterday.

The advertisement, which carried the sentence "Today's Peak Sauce Index is looking deliciously high", was published the day Singapore experienced its worst day of haze.

Said student King Rachel, 22: "If the advertisement had been used when the PSI first came up, the joke might seem funny. But when the PSI hits 300, it is not a joke any more."

But others on ST's Facebook page felt it was "clever" and chided critics for "not having a sense of humour".

In a statement yesterday, a spokesman for the fast-food chain said the one-off advertisement was "not intended to trivialise the current haze situation".

She added that it was designed and placed when haze conditions were not as severe. She also agreed that in this current context, the ad was "inappropriate".

"We are truly sorry that it has led people to feel that way," the spokesman said. "We share the concerns of Singaporeans and were equally surprised to see PSI levels hit record highs overnight."

FARAH MOHD ISMAIL