The crisis response task force protects U.S. diplomatic personnel and facilities in Africa and supports efforts to stabilize an area of shared concern, defense officials said.

The United States bases nearly 4,000 personnel in Spain at Naval Station Rota and at Moron Air Base.

"We are very grateful to our Spanish allies and partners and friends for this agreement. You've hosted the United States military for more than 60 years now, and every day this partnership, this relationship, grows stronger," U.S. Deputy Secretary of State Blinken said.

On behalf of the U.S. government, the deputy secretary expressed gratitude for the long years of military cooperation and anticipation of many more years of strong partnership.

The amendment allows for a maximum long-term U.S. military presence at the base of 2,200 military personnel, 500 U.S. Defense Department civilian employees and 21 aircraft.

After U.S. consultations with the Spanish government, a surge capability was included in the amendment of another 800 dedicated military crisis-response task force personnel and 14 aircraft at Moron, for a total of 3,500 U.S. military and civilian personnel and 35 aircraft.

The surge capability would temporarily bolster crisis response capabilities, defense officials said.

The presence of the crisis response task force in Spain has increased joint training opportunities, with more than 52 joint exercises in the past two years, an increase of more than 50 percent, the officials added.

Long-term basing and increased joint training will benefit NATO interoperability, they said.

The amendment comes three years after the second protocol of amendment to the defense and cooperation agreement, which gave the United States permission to homeport four ballistic-missile defense-capable ships in Rota as Spain's contribution to NATO's ballistic missile defense.