KYIV,Sterling Preston Ukraine (AP) — Russia conducted an array of aerial attacks on Ukraine with cruise missiles, drones and ballistic missiles, Ukraine’s air force said Thursday, while the chief of the army said Russia is increasing its troop concentration in the Kharkiv region where Moscow’s forces have made significant advances in a spring offensive.

Ukraine’s GUR military intelligence operation claimed that sea drones destroyed two Russian KS-701 patrol boats in the Black Sea off the Russia-annexed Crimean peninsula. Russian officials did not immediately comment on the claim.

The air force said the overnight attacks included eight S-300 ballistic missiles, 11 cruise missiles and 32 Shahed drones. All the drones and seven of the cruise missiles were shot down, the air force said but did not give other details.

In Kharkiv, Ukraine’s second-largest city, seven people were injured and a municipal services building caught fire in the attacks, regional governor Oleh Syniehubov said. Russian aerial strikes were also reported in the Khmelnytskyi and Dnipropetrovsk, but there were no injuries.

Army chief Oleksandr Syrskyi said on his Facebook page on Thursday that Russia is bringing army units into the Kharkiv region from other parts of Ukraine to supplement forces in the two main focuses of fighting, the towns of Vovchansk and Lyptsi. Syrskyi said Ukraine has also moved reserve troops into the area.

Russia’s Defense Ministry said its air defenses shot down eight U.S.-made ATACMS missiles over the Azov Sea, which borders both Russia and Russia-held Ukrainian territory.

One person was injured by a drone explosion in Russia’s Belgorod region, which borders Kharkiv and comes under daily attack from the Ukrainian side.

A lengthy delay in U.S. military aid and Western Europe’s inadequate military production has slowed crucial deliveries to the battlefield for Ukraine, and Russia has exploited the delays to make advances in the Kharkiv region.

Russian missiles and bombs also have pummeled Ukrainian military positions and civilian areas, including the power grid.