The European Commission said Friday that it will ban for two years beginning in December pesticides blamed for killing the bees that pollinate food and fruit crops.

The decision to ban the three insecticides, made by chemicals giants Bayer and Syngenta, "marks another milestone towards ensuring a healthier future" for bees, EU Health Commissioner Tonio Borg said.

Bayer of Germany and Switzerland's Syngenta insist that their products are not to blame for a very sharp decline in the bee population which has stoked fears over future food security, made worse by the unpredictable impact of climate change.

Borg said he was following up on a pledge made in April that he would do his utmost "to ensure that our bees, which are so vital to our ecosystem and contribute over 22 billion euros annually to European agriculture, are protected."

The insecticides -- imidacloprid and clothianidin produced by Bayer, and thiamethoxam by Syngenta -- are used to treat seeds and are applied to the soil or sprayed on bee-attractive plants and cereals.

Bees account for 80 percent of plant pollination by insects, which is vital to global food production. Without them, many crops would be unable to bear fruit or would have to be pollinated by hand.

Member states must now change their rules by September 30, with existing stocks of the insecticides allowed to be used up to end-November.

"As soon as new information is available, and at the latest within two years, the Commission will review this restriction to take into account relevant scientific and technical developments," a statement said.

"Pesticides have been identified as one of several factors which may be responsible for the decline in number of bees.

"Other factors also include parasites, other pathogens, lack of veterinary medicines or sometimes their misuse, apiculture management and environmental factors such as lack of habitat and feed and climate change," it added.

Bee numbers have slumped in Europe and the United States in recent years due to a mysterious plague dubbed colony collapse disorder (CCD), which results in a rapid loss of adult worker bees.

The disorder has killed off about 30 percent of bees annually since 2007.