The World Health Organization (WHO) is investigating whether there is any connection between manufacturers whose contaminated cough syrups it has linked to the deaths of more than 300 children in three countries.

Citing "unacceptable levels" of toxins in the products, the WHO is seeking more information about the specific raw materials used by six manufacturers in India and Indonesia to produce medicines linked to the recent deaths, as well as whether the companies obtained them from some of the same suppliers, a person familiar with the matter told Reuters.

The WHO has not named any suppliers.

The WHO also 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, the person said.

WHO experts are evaluating the evidence for whether, or when, such products are medically necessary for children, the person said.

The deaths of children from acute kidney injury began in July 2022 in Gambia, followed by cases in Indonesia and Uzbekistan.

The WHO has said the deaths are linked to over-the-counter cough syrups the children took for common illnesses and which contained a known toxin, either diethylene glycol or ethylene glycol.

To date, the WHO has identified six drug makers in India and Indonesia who produced the syrups.

These manufacturers have either declined to comment on the investigation or denied using contaminated materials that contributed to any deaths.

Reuters has no evidence of wrongdoing by the companies the WHO has named.

"This is of the highest priority for us, to see no more child deaths from something that is so preventable," WHO spokeswoman Margaret Harris said, without commenting further on the details of the organisation's work.

The United Nations health agency said on Monday it had widened its investigation into potential diethylene glycol and ethylene glycol contamination in cough syrups to four additional countries where the same products might have been on sale: Cambodia, the Philippines, East Timor and Senegal.

It called on other governments and the global pharmaceutical industry to launch urgent checks to root out substandard medicines and improve regulation.

The International Federation of Pharmaceutical Manufacturers and Associations (IFPMA) said in an emailed statement on Tuesday its members "are already doing what the WHO is calling for", in line with national and international guidelines.

The WHO is expected to comment further on the cough syrup situation during a news conference later on Tuesday.