A senior US defense department official says Russian artillery units are joining forces around Kyiv in an apparent move to attack the Ukrainian capital from afar.

The official presented the department's latest analysis on Russia's invasion of Ukraine on Thursday.

The official said there has been basically no change in the Russian forces around Kyiv, but Russia is moving some of those forces, including artillery units, from their rear to join their advancing elements, which the official said are 15 kilometers from the city center.

The official said the military continues long-range firing into Kyiv, trying to wear the city down. The official said it appears that the military still wants to seize the capital and is trying to improve its ability to hit cities from afar with munitions.

The official said Russian troops have seized the town of Izyum in eastern Ukraine and they want to continue to go south. The official said Russia's continued naval activity has been observed in the Black Sea, but there have been no imminent signs of an amphibious assault on Odesa, the largest port city in Ukraine.

The official said Russia's military has fired more than 1,000 missiles so far, and there has been an increase of strikes on civilian targets.

The official said his department has "anecdotal indications that Russian morale is flagging," and that the military faces a shortage of fuel and other necessary supplies for its campaigns.