Gentiva said it got a $17.25 per share buyout offer from "a recognized owner, operator and investor in the sector" on Thursday.

The offer values Gentiva at about $634.2 million based on the 36.8 million shares outstanding as of March 7.

Gentiva's shares rose 12 percent to $17.35 in extended trading, while Kindred's shares were flat with their close of $24.42 on Thursday.

The new offer, which was accompanied by support letters from major financial institutions, is based on publicly available information and is subject to financing and due diligence, Gentiva said.

Earlier this week, Kindred had raised its hostile bid to $16 per share for a 14.9 percent stake in Gentiva, stepping up its pursuit of the services provided by Gentiva to an aging U.S. population.

The stake would make Kindred the company's largest single shareholder. Gentiva last month adopted a "poison pill" with a trigger of 15 percent.

Gentiva on Thursday recommended its stockholders not to tender their shares to Kindred's "coercive" offer, saying it undervalued the company.

Kindred's stake would only be used as an "irritant designed to distract Gentiva from executing on its value-creating strategic plan or a potential impediment to any alternative transactions", Gentiva said.

Barclays and Edge Healthcare Partners are Gentiva's financial advisers and Greenberg Traurig, LLP is its legal adviser.