Private equity firms KKR and Stonepeak Partners raised their offer for Britain's Assura on Wednesday to almost 1.7 billion pounds ($2.3 billion), topping a rival bid with their "best and final" offer for the healthcare real estate investor.

The 52.1 pence a share offer, including dividends, trumps the 51.7 pence proposed by rival suitor Primary Health Properties last month.

It represents a more than 39% premium to Assura's closing price on February 13, the day before KKR and Stonepeak's first approach. The stock has soared 32% since then, giving Assura a market capitalization of 1.6 billion pounds as of Tuesday.

Assura manages over 600 healthcare properties with an investment value exceeding 3 billion pounds, and counts Britain's state-backed National Health Service as a customer.

It joins a growing list of UK companies being bought out by overseas private equity firms or investment companies, attracted by comparatively cheap valuations.

The latest all-cash offer "is lower risk than other alternatives" and requires no divestment, KKR Managing Director Andrew Furze said in a statement.

In April, Assura had backed KKR-Stonepeak's previous cash offer, prompting a higher bid from PHP last month. Some analysts had said PHP's offer was more attractive as it comprised cash and stock, and provided ownership of social healthcare assets via a public limited company listed in the UK.

PHP did not immediately respond to a request for comment.

($1 = 0.7415 pounds)

(Reporting by Yadarisa Shabong and Shashwat Awasthi in Bengaluru. Editing by Janane Venkatraman and Mark Potter)