WASHINGTON (AFP) - The US government on Monday granted Delta Air Lines and Virgin Atlantic Airways antitrust immunity for their proposed transatlantic joint venture, saying it would likely boost competition.

The Department of Transportation (DOT) said it had approved the request from the two airlines for protection from prosecution over antitrust issues.

"We have concluded that, overall, the alliance and joint venture will be pro-competitive and are likely to generate substantial public benefits to the traveling public," DOT said in its order.

In June, US and EU antitrust authorities approved Delta Air Lines' proposed purchase of a 49 per cent stake in Virgin Atlantic to build a joint transatlantic service, after determining the deal would not hurt competition.

But the venture also had sought the Department of Transportation's grant of immunity from any possible anti-trust action under US law against the venture.

In December, Delta announced it would buy the stake from Singapore Airlines for US$360 million (S$451 million), with the Virgin Group retaining its 51 per cent share.

The deal will put Delta and Virgin Atlantic into a joint venture which will offer as many as 31 round-trip flights between Britain and the United States, including 23 to or from the key London-Heathrow hub.

Delta and Virgin argued that their tie-up would offer more competition to American Airlines and British Airways, whose own cooperation holds a powerful share of the US-Heathrow market.