(Reuters) -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 Br…