The US-backed bidder for Morrisons has increased its offer for the supermarket group by £400m to £6.7bn in an attempt to fend off a rival suitor and win over reluctant shareholders. Fortress, the owner of Majestic Wine, which is owned by the Japanese investment company SoftBank, said on Friday that it was raising its bid to 270p a share plus a further 2p a share special dividend as it was “committed to becoming the new owner of Morrisons”. The higher offer for the UK’s fourth-largest supermarket comes as hopes of a further development in the bidding war increased late on Friday. Morrisons said it had asked the Takeover Panel to give private equity group Clayton, Dubilier & Rice more time to consider a bid to rival Fortress by extending a “put up or shut up” deadline of Monday at 5pm. Morrisons said it has adjourned a meeting at which shareholders will vote on the Fortress bid to 27 August, 11 days later than previously planned. The latest events follow Morrisons’ biggest shareholder, Silchester International Investors, which owns a 15% stake, saying that it was “not inclined to support” the Fortress group’s initial 254p a share bid. The fund manager said Morrisons’ board, which recommended the Fortress offer last month, should “allow more time to respond to other parties who might offer better value to Morrison’s public shareholders”. A lack of support from such a significant shareholder could make it difficult for the deal to gain the required approval from investors representing 75% of Morrisons’ shares. Morrisons’ board said it had unanimously recommended the new Fortress bid as it was “in the best interests of Morrisons shareholders as a whole”. The retailer’s share price, which began Friday at 271p in expectation that a better offer would emerge, jumped to almost 279p on news of the increased Fortress bid, its highest level since 2013. One person close to the process said CD&R, who are advised by former Tesco boss Terry Leahy, was likely to have a retort to Fortress by the Monday deadline. “I don’t think the endgame has been reached,” he said. Fortress’s bid is backed by the Canada Pension Plan Investment Board and the Koch family – the billionaire US industrialists who are known for their libertarian and conservative activism. Singapore’s sovereign wealth fund, GIC, also joined the consortium late last month, giving it extra firepower. A third potential bidder, Apollo Global Management, has said it no longer plans to make its own bid for Morrisons but is in discussions about teaming up with Fortress. CD&R kicked off the battle for Morrisons in June, when its £5.5bn offer, of 230p per share, was rejected by the company. The Fortress consortium made its initial £6.3bn bid at the start of July, which was approved by the Morrisons board but has run into trouble with some shareholders including Silchester. Another investor, Legal & General Investment Management, warned in July that Morrisons should not be bought for the “wrong reasons”, such as taking advantage of a possibly undervalued property portfolio, to load it up with debt, or to cut its tax bill.