United Parcel Service Inc. says it has agreed to buy TNT Express NV for $6.77 billion in a deal supported by TNT's boards.

UPS's cash offer of €9.5 per share for TNT — Europe's second-largest express delivery company behind DHL — comes a month after TNT turned down a €9 per share offer. The companies remained in talks.

UPS said Monday the deal is a 54 percent premium to TNT's closing price before the first offer Feb. 17. TNT shares closed at €9.35 on Friday.

The acquisition would be the biggest ever for Atlanta-based UPS, which is the world's largest delivery company.

Tags: UPS, United Parcel Service, TNT EXPRESS, Delivery companies