Police arrested 12 more people Thursday as China expanded a crackdown in a scandal involving tainted milk powder as a fourth death was announced and more than 6,200 other babies were sick from the powder.

The government in the Xinjiang region said a person died there after taking tainted milk powder. A notice on the government Web site did not say if the victim was a baby. The other three deaths were infants.

Meanwhile, dozens of parents, some cradling babies, lined up outside the Hebei province headquarters of the dairy company whose milk powder has been linked to most of the illnesses. They wanted refunds.

The dozen arrests throughout the province brought the total in custody to 18, said Shi Guizhong, spokesman for the Hebei provincial police.

Six people are accused of selling the industrial chemical melamine. Suppliers to the dairy companies are believed to have added the banned chemical, normally used in plastics, to watered-down milk to make it appear higher in protein.

The other 12 people arrested were milk suppliers accused of selling contaminated milk.

Shi said Hebei police and government officials were starting a 10-day campaign to focus on melamine contamination.

Police also confiscated 660 pounds of suspected chemicals, including 490 pounds of melamine, he said. An additional 87 people were summoned for questioning and 28 people have been detained, according to Shijiazhuang Vice Mayor Zhang Meizhi.

One suspect, surnamed Su, told police that from February 2007 to July 2008 he bought 200 44-pound sacks of melamine $29 each, and sold them all to milk suppliers, Shi told a news conference.

A transcript of the conference was posted on the Hebei government's Web site.

Shijiazhuang, Hebei's capital, is the headquarters for Sanlu Group Co. The parents gathered outside the office to get refunds for their purchases of tainted milk powder.

The mood was calm but confusion prevailed as parents traded tips on what products they thought were safe.

A 30-year-old mother who gave only her surname Wang said her 1-year-old daughter seemed healthy but that she was still worried. The three major milk powder brands that she usually buys — Yili Industrial Group Co., Mengniu Dairy Co. and Sanlu — have all been recalled.

"Of course as a mother, I was really nervous," she said. "Now we have no idea what kind of milk to give the baby. They all have problems."

The widening crisis has raised questions about the effectiveness of tighter controls China promised after a series of food safety scares in recent years over contaminated seafood, toothpaste and ingredients for pet food.

Authorities in Singapore announced they were recalling an ice cream bar made by Shanghai Yili AB Foods after melamine was found in it. Singapore said it would conduct tests on other imported milk and dairy products from China for contamination.

Hong Kong newspapers reported that many mainland residents were crossing the border to buy infant milk. Store owners said stocks were running low, but that there has been no panic buying.

China's government has dispatched thousands of inspectors to monitor milk powder producers after health officials reported Wednesday that the number of babies sickened by tainted formula rose to 6,244.

In addition to the four deaths, more than 1,300 other children, mostly newborns, remain hospitalized with 158 suffering from acute kidney failure, according to Health Minister Chen Zhu.

It is the second major case in recent years involving baby formula. In 2004, more than 200 Chinese infants suffered malnutrition and at least 12 died after being fed phony formula that contained no nutrients.

In a sign of the government's concern, Premier Wen Jiabao presided over a meeting Wednesday of China's Cabinet to back plans for a national inspection of milk products, according to a notice on the government's Web site.