Kuwait-based National Aviation Services (NAS) said on Thursday it had bought a 13.2% stake in John Menzies for 73.4 million pounds ($100 million), sending shares of the British airport services group soaring as investors bet on a sweetened bid.

John Menzies last week rejected a roughly 469 million pound ($638.64 million) takeover proposal from NAS, which it said undervalued the company. 

It said on Thursday it had not received another offer from NAS.

NAS said its affiliate Agility Strategies bought about 12.1 million shares in John Menzies, making it the company's biggest shareholder. It paid 605 pence each - compared with last week's 510 pence per share takeover bid.

On Thursday, John Menzies' shares closed nearly 25% higher at 584 pence.

Following the share purchase, NAS' future proposals for Menzies have to be higher than 605 pence per share under British regulations.

"Once again, we urge the Menzies board to engage with us so that we can put our compelling and deliverable offer to shareholders and secure Menzies' future in a highly uncertain environment," NAS Chief Executive Officer Hassan El-Houry said in a statement. 

The British group reiterated that it would "consider the best interests of Menzies' shareholders and all actions to maximise shareholder value".

John Menzies, like others in the aviation sector, is recovering from the impact of the pandemic. It suffered heavy losses in 2020 when lockdowns limited travel.

NAS, a unit of Kuwait's Agility Public Warehousing Co, has until March 9 to decide whether it wants to pursue the British company or walk away.

($1 = 0.7344 pounds)

(Reporting by Amna Karimi, Pushkala Aripaka and Sinchita Mitra in Bengaluru; Editing by Ramakrishnan M. and Barbara Lewis) ((Amna.karimi@thomsonreuters.com; +91 8083261226))