China's Anbang Insurance Group Co has raised its offer for Starwood Hotels & Resorts Worldwide Inc (HOT.N) to almost $14 billion, in its latest challenge to the U.S. hotel operator's merger with Marriott International Inc (MAR.O).

The bidding war for Starwood has pitted Marriott's ambitions to create the world's largest lodging company with about 5,700 hotels against Anbang's drive to create a vast investment portfolio of high-yielding U.S. real estate assets.

The acquisition of Starwood by Anbang would be the largest ever by a Chinese company in the United States.

Anbang's consortium, which includes private equity firms J.C. Flowers & Co and Primavera Capital Ltd, had offered $82.75 per share in cash, in what is reasonably likely to lead to a proposal that is superior to the deal with Marriott, Starwood said on Monday. Reuters had reported earlier on Monday that Anbang had raised its offer.

Marriott's latest cash-and-stock offer, which was announced on March 21, is currently worth around $78 per share. Starwood's board has not yet changed its recommendation to its shareholders in support of the company's merger with Marriott, Starwood said.