The European training center to teach Ukrainian pilots how to operate F-16 combat planes was officially opened on Monday in Romania.

“The center will be an international hub for the training of F-16 pilots and will facilitate increased interoperability among allies,” the Romanian defense ministry said. It was inaugurated by Romanian Defense Minister Angel Tîlvăr and his Dutch counterpart Kajsa Ollongren at an air base east of Bucharest.

Ukrainian President Volodymyr Zelenskyy said the training center is “a significant practical contribution to our aviation coalition.”

Kyiv has long argued it needs fighter jets to make significant military progress against Russia, which launched a full-scale invasion of Ukraine in February 2022. Denmark, the Netherlands, Norway and Belgium have announced they are willing to give U.S.-made F-16s to Kyiv.

Danish Defense Minister Troels Lund Poulsen said in October the first jets would be sent by April 2024. Belgium pledged to deliver the fighters by 2025, as long as the next government agrees after an election next year.

Last week, five Dutch F-16s arrived at the training center in Romania. Overall, the Dutch government will make between 12 and 18 aircraft available for training. “The training center in Romania will first use the aircraft to provide a refresher course for the hired F-16 instructors, after which training will be provided to the Romanian and Ukrainian pilots. The aircraft will only be flown in NATO airspace,” the Dutch government said.

In October, American Defense Secretary Lloyd Austin said the U.S. would head up the coalition of countries training Ukrainian pilots and crews to operate and maintain F-16 fighter jets alongside the Netherlands and Denmark.

Lockheed Martin, the U.S. company which manufactures the fighter jets, will contribute to providing training and maintenance.