NASA officials said Saturday that the launch of shuttle Endeavour would be delayed by at least four days after discovering a gas leak a few hours before lift-off, making it the second leak this year.

NASA had been planning liftoff for the Endeavour at 7:17 a.m. The launching was called off at 12:26 a.m. and the 16-day mission will be delayed until at least June 17, according to its website.

A similar leak occurred during the countdown for the shuttle Discovery in March.

“It was eerily the same,” Michael D. Leinbach, the shuttle launch director, said at a news conference, according to New York Times.

Hydrogen is a commodity you just don't mess with, he added

After calling off the launch, NASA began draining Endeavour's external fuel tank to begin an investigation of the leak. A hydrogen gas leak also delayed the March launch of Discovery by four days. NASA said it has fixed the leak at a vent line but the space agency still hasn't determined the exact source of the leak.

If Endeavour doesn't launch before June 20, the mission will be delayed until July 11 because the late June and early July sun angle on the ISS would create heat issues for Endeavour.