Twenty-First Century Fox is holding talks with private equity and property firm Blackstone over making a joint bid to buy US media group Tribune, according to reports.

Citing people familiar with the matter, Bloomberg News said the all-cash bid would be funded by Blackstone, while Fox would contribute its TV stations to the joint venture.

Fox and Blackstone are hoping to beat a rival offer from Sinclair Broadcasting, the largest owner of TV stations in the US.

Talks between Fox and Blackstone are progressing ahead of a deadline this week for final bids, Bloomberg said.

Nexstar Broadcasting, a Texas-based firm that owns 170 local TV stations, has also approached Tribune, according to the Wall Street Journal.

A source told the Journal that Fox wanted to acquire Tribune to keep it off the hands of Sinclair.

Sinclair already owns a number of TV stations affiliated with the Fox network and buying Tribune would give it an even greater number of stations, strengthening its hand in negotiations with Fox.

The Financial Times newspaper said buying Tribune would give Fox more ways to exploit sports rights, especially the US National Football League.

Fox is also looking to clear regulatory obstacles in the UK towards buying the 61% of broadcaster Sky that it does not yet own for £11.7bn ($15bn).

Media watchdog Ofcom and the Competition and Markets Authority are investigating the deal and are due to report their findings later this month.

The European Commission cleared the transaction in April, saying it did not raise any competition concerns.

Fox News has come under pressure in the US after it emerged that its star presenter Bill O'Reilly had paid out $13m in settlements to five women over sexual harassment allegations.

O'Reilly was dropped by the network on 19 April after more than 50 sponsors pulled ads from his show, The O'Reilly Factor.