British no-frills airline EasyJet has rejected three informal takeover proposals from a US private equity firm, the latest totalling nearly £5 billion ($6.6 billion), the two sides revealed Monday.

Private equity firm Castlelake has called on investors in Easyjet to lobby the budget airline to accept its third takeover offer.

Castlelake put forward a third approach to acquire easyJet on June 20 worth 625p a share, but said this was rejected on June 21.

Castlelake had submitted a fourth approach for easyJet worth £6.50 a share.