(Reuters) - U.S. health insurer Aetna Inc (>> Aetna Inc) is close to buying rival Humana Inc (>> Humana Inc) and a deal could be signed as early as this weekend, Bloomberg reported, citing people familiar with the matter.

Humana has also received an offer from Cigna Corp (>> CIGNA Corporation), but Humana's board prefers the offer from Aetna, Bloomberg reported.

Aetna and Humana were in talks, a source familiar with the matter told Reuters on Thursday, adding that there was no certainty Aetna would prevail. Cigna is also in the running, a second source confirmed to Reuters.

Aetna made a formal cash-and-stock bid this week to buy Humana, Bloomberg said.

Humana, which had a market value of $27.59 billion as of Wednesday's close, and Aetna were not immediately available for comment. Cigna declined to comment.

Reuters has previously reported that Humana is in takeover talks with Aetna and Cigna.

Bloomberg said discussions between Humana and Aetna intensified in the past few days after it emerged over the weekend that rivals Anthem Inc (>> Anthem Inc) and Cigna had held merger talks of their own.

Anthem said on Saturday it had offered $47 billion in cash and stock for smaller rival Cigna, who rebuffed the offer the next day.

The intensifying talks come as insurers seek scale to trim administrative costs and negotiate lower prices with doctors, moves they say will make plans more affordable.

Aetna's shares jumped 4.3 percent to record high of $133.05 after the report, while Humana's shares were up 6.5 percent at $196.21 in afternoon trading.

Cigna shares rose 2.7 percent to a record high of $170.20, before giving up some gains to trade up 1 pct at $167.51.

(Reporting by Rosmi Shaji in Bengaluru and Olivia Oran and Gregory Roumeliotis in New York; Editing by Maju Samuel and Savio D'Souza)

Stocks treated in this article : Aetna Inc, CIGNA Corporation, Humana Inc, Anthem Inc