The first flight test of Starship planned on Monday was postponed, according to the SpaceX live webcast.

Liftoff of the giant rocket was called off just minutes ahead of the scheduled launch time because of a pressurization issue, SpaceX officials said.

The launch, which marks the first flight test of SpaceX's fully integrated Starship and Super Heavy rocket, was scheduled for 8:20 a.m. Central Time from the SpaceX Starbase in the U.S. state of Texas.

With just less than a few minutes to go in the countdown, a pressurant valve appeared to be frozen, according to Elon Musk, founder, CEO and chief engineer of SpaceX.

Later, SpaceX confirmed standing down from Monday's flight test attempt, saying the team is working toward the next available opportunity.

"Learned a lot today, now offloading propellant, retrying in a few days," Musk tweeted.

SpaceX later said on Twitter that its teams were "working towards Thursday, April 20" for a second launch attempt.

The launch comes after the U.S. Federal Aviation Administration on Friday approved SpaceX's launch of the nearly 120-meter-tall rocket from its Boca Chica Launch Site in Cameron County, Texas.

SpaceX's Starship spacecraft and Super Heavy rocket, collectively referred to as Starship, represent a fully reusable transportation system designed to carry both crew and cargo to Earth orbit, the moon, Mars and beyond.

Starship will be the world's most powerful launch vehicle ever developed, capable of carrying up to 150 metric tonnes fully reusable and 250 metric tonnes expendable, according to SpaceX.

"With a test such as this, success is measured by how much we can learn, which will inform and improve the probability of success in the future as SpaceX rapidly advances development of Starship," SpaceX tweeted.

To date, the SpaceX team has completed multiple sub-orbital flight tests of Starship's upper stage from Starbase, demonstrating an unprecedented approach to controlled flight.

The team has also conducted numerous tests of the Super Heavy rocket, which include the increasingly complex static fires that led to a full-duration 31 Raptor engine test, according to SpaceX.

For the first flight test, the team will not attempt a vertical landing of Starship or a catch of the Super Heavy booster.

NASA awarded SpaceX contracts worth billions of U.S. dollars to use Starship to ferry American astronauts to the surface of the moon under the space agency's Artemis program.

NASA has already announced plans to use a Starship to put astronauts on the lunar surface in 2025.

(With input from agencies)