The Pentagon said on Thursday it will end operations at 15 military bases across Europe and hand them back to their home governments due to tight budgets and a shift in strategic focus.

In Britain, the U.S. Air Force will leave RAF Mildenhall, withdrawing some 3,200 military personnel and their families around 2019. Operations will also be closed at RAF Alconbury and RAF Molesworth in Cambridgeshire, reported the BBC.

"I know that this will result in a reduction of our local host nation's workforces at some locations. I value the tremendous support they provided us for decades," U.S. Defense Secretary Chuck Hagel said.

U.S. operations will also be halted at bases in Germany, Belgium, the Netherlands and Italy.

The decision was made in part due to budget constraints, and will save roughly $500 million per year, and partly because the Pentagon is shifting its attention toward the Asia-Pacific region, according to Reuters.

After being ordered to reduce spending by nearly $1 trillion over the next decade, the Pentagon has repeatedly asked Congress to close some facilities in the U.S., where there are believed to be 20 percent more bases than necessary. But lawmakers have resisted, telling defense officials to first close excess facilities in Europe.

Assistant Defense Secretary Derek Chollet said that while the changes would reduce support infrastructure, the U.S. military's operational capacity in the region would not be affected, reported the BBC.

"These ... adjustments do not diminish our ability to meet our commitments to allies and partners," Chollet said during a briefing. "In fact, these decisions will produce savings that will enable us to maintain a robust force presence in Europe."

The U.S. currently has around 64,000 troops stationed in Europe, with most concentrated in Germany, Italy and Britain.

The decision comes shortly after NATO announced that its main goal for 2015 is to build a rapid-response military force in Europe capable of deterring any possible Russian aggression.