Jeff Bezos' space company Blue Origin on Wednesday slammed Elon Musk’s SpaceX’s Starship, which would transport NASA astronauts to the lunar surface, calling the lunar starship “immensely complex & high risk.”

The comments came in an infographic on Blue Origin's website and amid tension between the two sides after NASA awarded SpaceX a highly coveted $2.9 billion contract.

The infographic goes over the differences in the two companies' rocket models and calls out Musk's Starship rocket for having “never conducted an orbital launch.”

SpaceX is in its final process before its first launch attempt.

“There are an unprecedented number of technologies, developments, and operations that have never been done before for Starship to land on the Moon,” read Blue Origin's comments.

Blue Origin's criticism comes after the Government Accountability Office on Friday determined that it was legal and appropriate for NASA to confer the sole contract to SpaceX.

Blue Origin has been at odds with NASA, saying the agency ran “an inconsistent and unfair competition,” as well as "a flawed acquisition and ignored the significant risks of a one provider model.”

Meanwhile, Blue Origin is asking NASA to give it a second contact under the original Human Landing System acquisition structure. Such a contract is expected to have a price well below the $2.9 billion awarded to SpaceX.

The Twitter account for SpaceX had three retweets between Monday and Wednesday from Musk, who posted pictures and videos of the rocket.