WATCH | More explosives found after Russia bombed its own city

Seventeen apartment buildings were evacuated Saturday in a Russian city near the Ukrainian border after an explosive device was found at the site where a bomb accidentally dropped by a Russian warplane caused a powerful blast this week, authorities said. 

The bomb blast late on Thursday rocked part of Belgorod, leaving a large crater and three people injured. The Russian Defense Ministry quickly acknowledged that a weapon accidentally released by one of its own Su-34 bombers caused the explosion. 

On Sunday, Russia announced it was expelling more than 20 German diplomats in a tit-for-tat move. Germany did not immediately confirm any expulsions of its own, but said the arrival of a Russian government plane in Berlin was connected to the issue, Reuters reported.

Russia's RIA Novosti news agency said Germany had decided to expel more than 20 Russians.