Adm. Charles Richard, commander of the U.S. Strategic Command, said Thursday that the first two missile fields being built are part of China‘s “explosive” expansion of nuclear forces.

“We are witnessing a strategic breakout by China,” Adm. Richard told a missile defense conference in Alabama. “The explosive growth in their nuclear and conventional forces can only be what I described as breathtaking,” he said, adding that “frankly, that word ‘breathtaking’ may not be enough.”

Adm. Richard said the two new missile fields recently disclosed in published reports will include silos for more than 100 nuclear land-based intercontinental ballistic missiles. He suggested that additional missile bases are under construction.