Alaska’s congressional delegation expressed concern Thursday about the Pentagon’s decision to cancel a project designed to improve ground-based interceptor missiles, raising questions about additional missiles set to be housed at Fort Greely outside Fairbanks.

The Pentagon canceled the Boeing contract for the project last week amid concerns about unstated design flaws associated with the missiles, which are designed to strike down incoming threats as North Korea, China and Russia take steps to advance their missile capabilities.

Congress had authorized the Pentagon to add 20 updated interceptor missiles to the current fleet of 44. Most of the current fleet is housed in three missile fields at Fort Greely, southeast of Fairbanks.

Sen. Lisa Murkowski said in a statement that it makes sense to see the U.S. military adapting to new threats. But she said it’s “disappointing” the contract was canceled before the additional 20 ground-based interceptors were placed in Alaska.

“I will demand answers so that we fully understand the rationale behind this decision,” she said. "It is my understanding that construction of Missile Field Four at Fort Greely will continue, and once the next-generation interceptors are built, I will work to ensure that those will be placed in Alaska to serve as our nation’s first line of defense.”

The 20 planned missiles were to be equipped with improved “kill-vehicles,” devices released from the airborne missiles to strike and disable incoming threats.

Sen. Dan Sullivan, a member of the Senate Armed Services Committee, said he’s “deeply concerned” about the Pentagon’s change of plans, according to a statement from his office.

“Given the continued evolution of advanced adversaries’ missile capabilities and still uncertain and unpredictable nature of North Korean leader Kim Jong Un, we cannot afford to wait possibly a decade for a new and still conceptual kill vehicle,” he said. “I plan to dig deep into the assumptions made and details of the decision-making undertaken that led to what I hope is not this short-sighted decision.”

Rep. Don Young called the decision to cancel the redesigned kill vehicle program “troubling," according to a statement.

“When it comes to our national defense posture, Alaska is an important strategic location for keeping Americans safe," he said. "Our national defense cannot wait for a new kill vehicle program to be developed, and it is one of my highest priorities to see a new kill vehicle swiftly designed and implemented.”