Russian border officials were sent to the Rostov Province today to investigate reports of cross-border fire by Ukrainian military forces. The trip did not go well, and Russia is now accusing Ukraine’s military of trying to kill the investigators.

According to Russian accounts, some 40 shells fired by Ukraine’s military fell in the Rostov Province, including 30 that fell in a village that the investigators were visiting, forcing them to flee in armored vehicles.

Cross-border fire is becoming a growing allegation on both sides, with Ukraine’s government countering by claiming the Russian military was shelling their forces during battles with eastern rebels, trying to support the rebel counter-attack.

Russia has denied the claims of directly arming the rebels, but have warned the Ukrainian government against their continuing offensives against east Ukraine, predominantly ethnic Russian. Some 250,000 Ukrainians have fled into Russia as a result of the military operation.