Monsanto (MON.N), the world's largest seed company has again approached Switzerland's Syngenta (SYNN.VX) in recent weeks with an offer to buy the company, Bloomberg reported citing people familiar with the matter.

However, the Swiss crop chemical maker has concerns as the merger would raise antitrust concerns, Bloomberg said.

The two companies may again fail to reach an agreement, Bloomberg said.

According to media reports, Monsanto and Syngenta had held preliminary talks last year about a $40 billion takeover by Monsanto to create the world's largest agrochemical company.

Monsanto spokeswoman Sara Miller said the company does not comment on rumors or speculation.

Syngenta could not be immediately reached for comment outside regular business hours.