A clash between Ukrainian security personnel and pro-Russian separatists ended with at least eight security personnel dead and 18 wounded three days before Ukrainians head to the polls to elect their next president.

The violence broke out about 12 miles south of Donetsk, which is controlled by pro-Russian separatists and is Ukraine’s fifth-largest city, officials told Reuters on Thursday. Ukraine’s defense ministry confirmed the firefight but did not give an exact number of casualties. They said the violence erupted when pro-Russian separatists opened fire on an army checkpoint near Volnovakha.

Another clash occurred in a neighboring region, but there was no immediate word of any casualties.  

Several guards were hurt in fighting between security forces and pro-Russian separatists armed with grenade launchers and rifles who entered the Luhansk region overnight from Russia, Ukrainian border guards told Reuters.

There has been an uptick in violence in eastern Ukraine in recent weeks as Ukraine’s pro-Western interim government deals with a breakdown in security. Kiev accused Moscow of attempting to undermine the country’s presidential election, a view also held by the European Union and the United States. Meanwhile, Russia hasn’t recognized Ukraine’s government since it came to power during the February Euromaidan protests that led to the ouster of pro-Russian President Viktor Yanukovych, who fled to Russia, and the tensions between Ukraine and Russia intensified when Moscow took control of Ukraine-held Crimea in March.

Putin defended the move, saying Moscow has a responsibility to protect Russian-speaking peoples living outside Russia’s borders. Eastern Ukraine is sympathetic to Russia while the western portion of the country is strongly aligned with the West.