German chemicals giant Bayer said on Wednesday it had signed a $66 billion (58.8 billion euros) takeover deal with US genetically modified (GM) seeds firm Monsanto.

"Bayer and Monsanto have signed a binding merger agreement that enables Bayer to take over Monsanto for $128 per share," the firms said in a statement.

Bayer repeatedly increased its offer to Monsanto since its first $122-per-share bid in May, but the US firm had until now held out for more cash.