North Korea’s positioning of a rocket on its east coast launchpad has ratcheted up tensions with Washington on Thursday, which warned that pushing ahead with the April launch would violate a U.N. ban and have serious consequences.

Pyongyang says the rocket is designed to carry its Kwangmyongsong-2 satellite into orbit, an accomplishment timed for the eve of the inaugural session of North Korea’s new parliament and for late founder Kim Il Sung’s April 15 birthday.

But regional powers suspect the North will use the launch to test the delivery technology for a long-range missile, one capable of striking Alaska, or may even test-fire the intercontinental Taepodong-2 missile itself. Keeping speculation about the payload alive, North Korea reportedly has covered the top of the rocket.