Pro-Russian separatists in the eastern Ukraine city of Donetsk say a van used by separatist rebel leader Denis Pushilin exploded Thursday in the central city, injuring at least three bodyguards.
Rebels said Pushilin - one of the leaders of the self-proclaimed Donetsk People's Republic - was not in the vehicle when the blast occurred in front of a separatist-occupied building.
Also on Thursday, Ukraine Interior Minister Arsen Avakov accused Russia of allowing an armored column, including three military tanks, to cross into Ukraine at a border control point manned by separatists.
Russia did not immediately respond to the accusation, but reporters for Reuters news agency said three Soviet-era T-72 tanks were later seen in the Ukraine border town of Snizhnye.
It was not immediately clear whether Russian troops crossed into Ukraine with the tanks or whether the column was under rebel control.
Russia, which annexed Ukraine's Crimea peninsula in March, has repeatedly said it would not make further intrusions into Ukrainian territory.
In another development, Russian forces began military exercises Thursday in the Baltic Sea enclave of Kaliningrad. Moscow says the exercises are a response to ongoing NATO maneuvers in European NATO countries near its borders. Kaliningrad is a tiny Russian territory wedged between NATO member-states Lithuania and Poland.
In Moscow, meanwhile, Russian President Vladimir Putin marked one of Russia's main holidays, Russia Day, with praise for the annexation of Crimea. In an address, Mr. Putin said the peninsula and its strategic Black Sea port of Sevastopol have come back to their "homeland." He called the annexation a "historic reunification" and said it took place peacefully "and fully in line with the norms of international law."
Western governments and the United Nations say the peninsula has been occupied by Russian soldiers.