The Kingdom of Saudi Arabia intends to invest $1 billion in Virgin Group space companies, according to billionaire Richard Branson's conglomerate on Thursday.

The contract is described as a "partnership on spaceflight, satellite launch and space-centric entertainment," backed by the Public Investment Fund of Saudi Arabia. The venture will fuel three Virgin companies – Virgin Galactic, The Spaceship Company and Virgin Orbit – and includes an option for an additional $480 million.

"This partnership with Virgin Group reflects the great strides the Kingdom is making towards our vision for a diversified, knowledge-based economy," Saudi Crown Prince Mohammed bin Salman said in a statement.

In a post on Virgin's website, Branson wrote that the investment "is a sign of confidence from the international community" in the three companies, which he emphasized will remain based in the Southwestern U.S.

"We are now just months away from Virgin Galactic sending people into space and Virgin Orbit placing satellites around the Earth," Branson said.

Tweet @richardbranson: Pleased Saudi Arabia intends to invest $1B in our space companies @virgingalactic @virgin_orbit @TheSpaceshipCo

Branson told CNBC last week that he is focused on using "space to benefit the Earth."

His space company, Virgin Galactic, has yet to send a manned craft into space — but that may soon change. He said the spaceship VSS Unity "should be in space in about four months."

Virgin Orbit is a further endeavor by Branson, which he spun off from Virgin Galactic to build air-launched rockets to send dozens of small satellites into orbit. Virgin Orbit's LauncherOne system is still in development. The company is planning the rocket's first test flight for early next year, with the system's Boeing 747-400 launcher in its final stages of flight testing.

Saudi Arabia's investment, subject to regulatory approval, would give the country "a significant stake" in the companies, but Branson says Virgin "will remain majority shareholders."