Ukraine’s President Volodymyr Zelenskyy has replaced one of his top security officials. Oleksii Danilov served as secretary of the National Security and Defense Council but was replaced late Tuesday with Oleksandr Lytvynenko, the head of Ukraine’s Foreign Intelligence Service. Zelenskyy didn’t announce the reasons behind the reshuffle. Danilov’s dismissal comes as exhausted Ukrainian troops struggle with a shortage of personnel and ammunition and are facing growing Russian pressure along the front line that stretches over 620 miles. In February, Zelenskyy replaced the country’s chief military officer.