TORONTO -- Border officials at Toronto's Pearson airport have seized more than 10 kilograms of suspected heroin stuffed inside a sport bag they say arrived on a flight from Pakistan.

Canada Border Services Agency says officers spotted a suspicious box July 2 while checking shipments as they were unloaded from the plane.

They say inside the cardboard box was a blue sports bag holding four small packages carefully wrapped with brown packing tape.

The agency says preliminary testing indicates the substance in the packages is likely heroin, and will now be sent off for further testing.

The investigation has been handed over to Peel police. There's no word yet on any suspects.

Regional director Goran Vragovic says the narcotic seizure is the second big drug bust at the airport in the last few weeks.

More than 18 kilograms of suspected cocaine were found by the agency last month tucked into a bathroom overhang.

"I want to warn would-be smugglers that CBSA officers will not tolerate the use of our international airports for illegal cross border activities," Vragovic said in a statement.