The Yonhap news agency quoted South Korea's military as saying at least one projectile was fired into the Sea of Japan.

quote sb. as saying... 援引某人的话称......

If you quote someone as saying something, you repeat what they have written or said. 引用; 引述

He quoted Mr. Polay as saying that peace negotiations were already underway.

他引用波利先生的话说，和平谈判已在进行。

as 为介词，as saying...作方式状语。

【翻译】韩国联合通讯社援引韩国军方的话说，至少有一枚炮弹射入日本海。