The EU is demanding further concessions in order to approve the proposed buyout of US agri-giant Monsanto by German chemical firm Bayer, a source close to the matter said on Monday.

Brussels launched an in-depth investigation in August into the $66 billion (56-billion-euro) deal, which would create the world's largest integrated pesticides and seeds company.

The European Commission, which serves as the powerful anti-trust regulator for the 28-nation European Union, cited concerns it could reduce competition in key products for farmers.

Brussels is also under pressure by environmentalists who fear that the deal would give too much power to the world's leading manufacturers of GMOs and the controversial weedkiller glyphosate.

The EU late last week lodged a statement of objections cataloguing potential reasons for the EU to block its proposed takeover, indicating more concessions were needed, the source told AFP.

These further concessions would be in addition to the announced sale in October by Bayer of parts of its agrochemical business to German rival BASF.

That deal would see Bayer sell the lion's share of its crop seeds units and its glyphosate herbicide business to BASF for 5.9 billion euros ($7 billion).

The deadline for the merger approval is currently March 5, but sources close to the matter said it could be further delayed.

Both Bayer and the commission refused to comment.