China has blamed Panamanian firms for passing off a Chinese industrial solvent for use in medicines, so causing dozens of deaths in Panama.
The Panamanian deaths began coming to light last September
A Chinese official said Panamanian firms doctored paperwork to mislabel the chemical's use and shelf life.
These comments come amid a series of health scares about Chinese products.
Nicaragua is the latest country to seize Chinese toothpaste tainted with diethylene glycol - the same chemical found in the Panamanian cough syrup.
Nicaraguan police confiscated more than 40,000 tubes of Chinese-made toothpaste, the country's health minister Maritza Cuan said on Thursday.
The Dominican Republic, Panama and Costa Rica had already pulled thousands of tubes of toothpaste from store shelves, and the US authorities have been checking shipments of toothpaste imported from China.
Diethylene glycol is an industrial solvent and is found in some antifreezes. It is also sometimes used as a low-cost but potentially deadly substitute for glycerine sweetener commonly used in medicines.
It was found in the medicines blamed for last year's deaths in Panama. At least 50 people are known to have died as a result with some reports saying the figure could be more than 100.
A senior official in Beijing, Wei Chuanzhong, said the chemical had been confusingly labelled as "TD glycerine" when Chinese companies sold it to Spanish firms. They then sold the product on to Panamanian firms.
He accused Panamanian traders of doctoring the records to show the product as medical glycerine which was then used in cough syrups and other medicines.
They also changed the shelf life of the already expired product from one year to four years, he said.
The Panamanian authorities this week ordered the arrest of three senior officials accused of involvement in the distribution of the tainted medicines.