Wheelock Properties and property tycoon Ong Beng Seng are dangling an even bigger carrot for shareholders of their buyout target Hotel Properties Limited (HPL), which they want to take private.

Their consortium, 68 Holdings, has agreed to buy 6.7 million shares in HPL - about a 1.29 per cent stake - for $4.05 apiece, HPL told the Singapore Exchange on Tuesday.

It has therefore upped its offer for the remaining shares it does not own to $4.05 apiece, valuing the hotel firm at about $2.1 billion.

HPL owns and operates properties in Singapore, Malaysia, Thailand and the Maldives, including the Four Seasons hotel and Forum the Shopping Mall.

This is the second time the consortium has raised its offer for HPL. It initially offered to pay $3.50 per share but increased the amount to $4 earlier this month, an amount that independent financial adviser CIMB Bank said was "fair and reasonable".

It may revise its offer amount yet again if a competing offer for HPL is announced, HPL said in its statement.

Mr Ong is the founder and managing director of HPL. His consortium started the takeover exercise last month after it bought about 41.91 per cent of HPL's shares for $3.50, triggering a mandatory conditional takeover of the firm.

The closing date of the offer has been extended from June 2 to June 12.