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) and hinted at a sweetened bid, sending shares of the British airport services group soaring 26%.

NAS said its affiliate Agility Strategies bought about 12.1 million shares in John Menzies at 605 pence apiece, becoming its biggest shareholder just days after the London-listed firm rejected NAS' lower takeover proposal. 

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

John Menzies did not immediately respond to a Reuters request for comment.

"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. 

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 = 0.7355 pounds)

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