CHANGCHUN - Chinese police said on Tuesday that the Coca-Cola brand milk drinks suspected of causing one death and sickening three others in Changchun, the capital city of northeastern Jilin province, were deliberately poisoned.

On Nov 28, a boy died and his mother was poisoned after having the flavored milk made by the Coca-Cola subsidiary Minute Maid in Jilin. The mother remains hospitalized, but she is in stable condition.

In a separate incident, two other Changchun residents were hospitalized after drinking the same product. They have been treated and discharged from hospital.

The two incidents have prompted the province to pull all of the Minute Maid products from shelves.

Police said samples taken from the problematic drinks contained Methomyl and thiodicarb -- substances used in pesticides.

Coca-Cola has entrusted the China National Center for Food Quality Supervision and Testing to test samples from the same batch of the strawberry-flavored milk drinks.

According to a report released by the center on Monday, no toxic substances have been found in these products.

A special work group, including seven experts from the Ministry of Public Security, are continuing the investigation.

Meanwhile, no information has been released explaining how the toxic chemicals were mixed into the drinks.

Coca-Cola said in a press release on Monday that the company has "100-percent confidence" that its products are absolutely safe and reliable.

However, this is not the first time that the US beverage giant has been involved in scandals involving tainted or poisonous products in China. In Beijing, two cases were reported in 2009 and 2010, respectively, in which a man and a teenager were suspected of being poisoned by mercury-tainted Sprite drinks.

Investigations later revealed the two cases were the result of intentional poisoning, and, therefore, were not a quality issue for Coca-Cola.