(Feb 13): Delta Air Lines Inc raised its offer to buy up to 32% of Grupo Aeromexico SAB de CV by more than a fifth on Monday, valuing the deal at about US$590 million.

Delta, which already has a 4.2% stake in Aeromexico, had said in November 2015 it intended to buy the additional stake for 43.59 Mexican pesos (US$2.15) per share.

The 53 Mexican pesos per share deal represents a premium of 34.4% to Aeromexico's Friday close.

Aeromexico had about 707.8 million shares outstanding as of Jan 25, according to Thomson Reuters data.

The Mexican airline's shares rose as much as 21.5% to 47.90 Mexican pesos in morning trading.

The increase in the purchase price was the result of interim exchange rate movements and other factors, Delta said.

If Delta exercises the share purchase options it holds, the stake could go up to 49%, the company said.