Bayer AG and Monsanto Co promised US president-elect Donald Trump $8 billion of investment in the United States and thousands of new jobs should the companies' planned merger, the biggest-ever in agriculture, clear regulatory approvals.

Bayer Chief Executive Officer Werner Baumann promised to add 3,000 jobs at Monsanto while keeping its headquarters in St. Louis after the deal is completed, Trump spokesman Sean Spicer said on Tuesday.

Both companies had previously announced their intention to keep the location of the Monsanto offices, but the commitment on jobs is new, and follows a visit last week by both Baumann and Monsanto CEO Hugh Grant to Trump and his aides in New York.

The CEOs said in a joint statement that "several thousand new high-tech, well-paying jobs" will be added after the integration of the two companies.

US businesses are facing more pressure to show that they're creating US jobs ahead of Friday's scheduled inauguration of Trump, who made the issue a signature of his campaign.

Earlier on Tuesday, he praised General Motors Co for a $1 billion US investment plan, having criticized the company earlier in January for importing some models from Mexico.

On Tuesday, Wal-Mart Stores Inc also boasted about job growth. Ford Motor Co and Fiat Chrysler Automobiles NV announced spending plans last week that Trump lauded.

The proposed $66 billion takeover of Monsanto by Germany's Bayer would create the world's largest producer of pesticides and genetically modified seeds.

A year ago, Monsanto announced that it would shed 3,600 jobs, or about 16 percent of its global workforce, in a bid to lower costs. The company is already the world's biggest seed producer.