* EFSA says neonicotinoids may affect developing human brain
* Warning comes after some insecticides linked to bee deaths
* Bayer says findings based on inconclusive evidence (Adds comment from Bayer, European Commission)
LONDON, Dec 17 (Reuters) - European health authorities warned on Tuesday that two insecticides, including a widely-used chemical made by Bayer, may affect the developing human brain and should be more tightly controlled to limit human exposure.
The products - acetamiprid and imidacloprid - belong to a popular class of insecticides called neonicotinoids, which have recently been in the spotlight due to links with plunging populations of bees. Imidacloprid is one of the most widely used insecticides in the world.
The European Union voted in April to ban three neonicotinoids - including imidacloprid which is primarily manufactured by Bayer - for two years amid safety and environmental concerns.
In Tuesday's move, the European Food Safety Authority (EFSA) recommended that guidance levels for exposure to the products be lowered while further research is carried out to provide more reliable data on so-called developmental neurotoxicity.
"Acetamiprid and imidacloprid may adversely affect the development of neurons and brain structures associated with functions such as learning and memory," EFSA said in a statement from its Rome headquarters.
"Some current guidance levels for acceptable exposure to acetamiprid and imidacloprid may not be protective enough to safeguard against developmental neurotoxicity and should be reduced."
A spokesman for the European Commission, which asked EFSA to carry out the assessment, said it would give Bayer and the makers of acetamiprid an opportunity to comment on the findings.
"In principle, the next step would then be to amend the reference values," said Commission health spokesman Frederic Vincent, adding that EU government officials would begin the process at a meeting in March.
In response, Bayer's CropScience division said it saw no link between imidacloprid and developmental neurotoxicity in humans, and said EFSA had based its concerns on an inconclusive 2012 study that used tests on rat cell cultures.
"EFSA itself recognises the limitations of this publication. Bayer CropScience has also evaluated the publication and can confirm that few conclusions can be drawn from it," the statement said. (Reporting by Kate Kelland, additional reporting by Charlie Dunmore in Brussels; editing by William Hardy and Tom Pfeiffer)