President Volodymyr Zelenskyy dismissed the secretary of Ukraine's national security council as he appointed the chief of the country's foreign intelligence agency on Tuesday.

No reason for the changes was given in a series of dryly worded decrees that were published on the president's website more than two years into Russia's full-scale invasion.

Oleksiy Danilov, the outgoing secretary of the National Security and Defence Council, had held his position since October 2019, just months after Zelenskyy took office.

Zelenskyy appointed Oleksandr Lytvynenko, 51, head of the foreign intelligence service, who has no almost public profile whatsoever, to head the council.

The council has a coordinating role on issues of national security and defense under the president and comprises the country's top political, security and defense chiefs.

Ukraine is battling to keep up its war effort and hold the line against attacking Russian forces in the east with its vital U.S. ally proving unable to deliver military assistance due to Republican congressional resistance.

Military analysts are also raising questions about the depth and strength of Ukrainian fortifications and regard manpower levels as another challenge. Russia has a much larger population than Ukraine and is on the offensive.

Zelenskiy's decrees named Oleh Ivashchenko, a deputy chief of the Ukrainian military spy agency who also has no public profile, as the new foreign intelligence chief.

The Ukrainian leader replaced the head of the armed forces in February. Swathes of the military's top brass were also cleared out and replaced.