Taipei ¨C Taiwan¡¯s Air Force has grounded its F-16 fleet after losing a plane on a training mission, President Tsai Ing-wen said on Wednesday, the second loss of a fighter jet in less than a month at a time of increased missions to intercept Chinese aircraft.

While the air force is well trained and well equipped, mostly with U.S.-made equipment, it is dwarfed by China¡¯s. Beijing claims the democratic island as its own and has never renounced the use of force to bring it under Chinese control.

Last month, Taiwan¡¯s defense minister said nearly $900 million had been spent this year on scrambling the air force against Chinese incursions, describing the pressure they are facing as ¡°great.¡±

Late Tuesday, Taiwan¡¯s Air Force said a U.S.-built F-16 vanished shortly after taking off from the Hualien air base on the east coast on a routine training mission.

That followed the crash of an F-5 ¡ª a jet which first entered service in Taiwan in the 1970s ¡ª in late October.

Speaking to reporters, Tsai said the air force had already grounded the F-16 fleet for checks.

¡°I have asked the Defense Ministry not to relax a bit on defense and combat readiness to ensure national security,¡± she added.

The Defense Ministry called on media not to speculate on what happened to the F-16, adding that missions needed to continue considering the ongoing threat from China.

¡°In response to the increasingly severe situation in the Taiwan Strait, the military has continued to strengthen combat readiness training to ensure national security,¡± it said.

The loss of the F-16 is Taiwan¡¯s fourth military crash this year. In January, Taiwan¡¯s top military official was among eight people killed after a helicopter carrying them to visit soldiers crashed in a mountainous area near the capital Taipei.

The United States last year approved an $8 billion sale of F-16 fighter jets to Taiwan, a deal that would take the island¡¯s F-16 fleet to more than 200 jets, the largest in Asia.