Scientists are looking for the presence of the insecticide fipronil, a substance potentially dangerous to humans, after supermarkets in Germany, the Netherlands, Belgium, Sweden and Switzerland pulled millions of eggs from the shelves.

"We are currently testing chicken meat in the poultry farms where eggs were infected to determine whether the meat is contaminated as well," said Tjitte Mastenbroek, spokesperson for food security agency NVWA.

The probe focuses on "a few dozen" farms that produce both eggs and chicken meat, NVWA said.

Millions of chickens now face being culled in the Netherlands as the scandal widens.

Hard-hit Germany on Tuesday called on Belgian and Dutch authorities to quickly shed light on what it termed a "criminal network" involved in the contamination of eggs with fipronil.

"When one sees a criminal energy that's almost organized as a network it's unacceptable," German Agriculture Minister Christian Schmidt said.

He again criticized Belgian and Dutch authorities' tardy response to the crisis.

'Highest priority'

Belgium's top agricultural official on Monday ordered the country's food safety agency to report within a day why it failed to notify neighboring countries until July 20 despite knowing about fipronil contamination since June.

"It's not in the spirit of the early warning system to be aware in June but only to inform us by the end of July," Mr Schmidt said.

Ms Mastenbroek said that a criminal probe by the NVWA under Dutch prosecution authorities and assisted by Belgium is continuing, looking at the role of companies in contaminating Dutch poultry farms with fipronil.

Mastenbroek said so far her agency's "highest priority" has been the detection of contaminated eggs.

"But now we also have the time to look at meat as a precautionary measure," she said.

Most farms exclusively produce one or the other, said Eric Hubers at LTO, a Dutch farming organization.

If the meat tests are negative for fipronil, producers will be cleared to resume sales, Ms Mastenbroek said.

LTO said the probability of chicken meat found to be infected was small.