BRUSSELS/FRANKFURT — The European Commission has started an in-depth investigation of Bayer's planned $66 billion takeover of U.S. seeds group Monsanto, saying it was worried about competition in various pesticide and seeds markets.

The deal would create the world's largest integrated pesticides and seeds company, the Commission said, adding this limited the number of competitors selling herbicides and seeds in Europe.

"The Commission has preliminary concerns that the proposed acquisition could reduce competition in a number of different markets resulting in higher prices, lower quality, less choice and less innovation," it said in a statement on Tuesday.