China’s air force sent 25 fighters and bombers over the Taiwan Strait, escalating military pressure on the Taiwanese government as Taipei boosts ties with the U.S.

Beijing deployed 14 J-16 and four J-10 fighters, four H-6K bombers, two Y-8 anti-sub warfare planes and one KJ-500 early warning aircraft into the southwest section of Taiwan’s air defense identification zone Monday, Taiwan’s Ministry of National Defense said in a statement.

The sortie was the largest China has sent toward Taiwan this year. The ministry said the Taiwanese air force responded by sending patrol aircraft to the area and tracking the Chinese planes with missile defense systems.