The World Health Organisation has thus far failed to track down the source of contaminated cough syrups sold in at least seven low-income countries, a spokeswoman says in Geneva.
It remained unclear whether counterfeit medications or contaminated juices used in the production were to blame, she said.
Industrial solvents and anti-freeze agents have been found that could be fatal to infants and young children.
The spokeswoman said the WHO was relying on governments to check how the contaminants had entered the supply chain and what needed to be done to prevent further occurrence.
"Accidents can happen. But it should not happen," she said.
On Monday, the WHO issued a call to countries "to prevent, detect and respond to incidents of substandard and falsified medical products," saying that over the past four months, there had been reports of contaminated over-the-counter cough syrups for children.
The cases were from seven countries and more than 300 fatalities were associated with the reports, most of them children under the age of five.
The countries with fatalities include Gambia, Indonesia and Uzbekistan.
Other countries with suspected cases are the Philippines, East Timor, Senegal and Cambodia.
The WHO is considering whether to advise families globally to reassess the use of cough syrups for children in general while questions over the safety of some of these products are unresolved, a source told Reuters.
WHO experts are evaluating the evidence for whether, or when, such products are medically necessary for children, the person said.