Ukraine utilizes US-provided cluster munitions in ongoing counteroffensive against entrenched Russian forces

Ukraine has begun using cluster munitions supplied by the US against Russian forces.
The weapons are controversial but seen as effective against Russian defenses.
Russia has threatened retaliation but has already used cluster bombs itself.
Ukraine's counteroffensive has progressed slower than expected due to stubborn Russian resistance.
Tensions remain high in the Black Sea region amid strikes on Ukrainian port cities.