In March 1944, UPA insurgents mortally wounded front commander Army General Nikolai Vatutin, who liberated Kyiv when he led Soviet forces in the Second battle of Kiev . Several weeks later an NKVD battalion was annihilated by the UPA near Rivne. This resulted in a full-scale operation in the spring of 1944, initially involving 30,000 Soviet troops against the UPA in Volhynia. Estimates of casualties vary depending on the source. A letter to the state defence committee of the USSR, Lavrentiy Beria stated that in spring 1944 clashes between Soviet forces and UPA resulted in 2,018 killed and 1,570 captured UPA fighters and only 11 Soviet killed and 46 wounded. Soviet archives show that a captured UPA member stated that he received reports about UPA losses of 200 fighters while the Soviet forces lost 2,000. The first significant sabotage operations against communications of the Soviet Army before their offensive against the Germans was conducted by the UPA in April–May 1944. Such actions were promptly stopped by the Soviet Army and NKVD troops, after which the OUN/UPA submitted an order to temporarily cease anti-Soviet activities and prepare for further struggle against the Soviets.