The United States in recent weeks secretly shipped long-range missiles to Ukraine for use in its battle to fight off Russian invaders, and Ukraine has now used them twice, a U.S. official said on Wednesday.

The missiles were contained in a $300 million military aid package for Ukraine that U.S. President Joe Biden approved on March 12, said the U.S. official, speaking on condition of anonymity.

The official would not say how many of the missiles were sent.