Russia's defense minister has announced new exercises in regions bordering on Ukraine. Russian President Vladimir Putin earlier said Kyiv's military operations in the east would "have consequences."
Russia's announcement that maneuvers near the border had been resumed came after clashes in eastern Ukraine, with the interior ministry in Kyiv saying it had killed up to five militants.
"We are compelled to react to such a situation," Russian Defense Minister Sergei Shoigu was reported as saying by domestic news agencies. "From today, military exercises have started in regions bordering on Ukraine involving battalions of tactical forces of the southern and western military districts," he said.
In addition to the ground troops, Shoigu said the air force would be patrolling the border.
The Ukrainian interior ministry had earlier said that the deaths of the pro-Russian militants had occurred during an "anti-terrorist operation on Thursday." It said Ukrainian troops had removed three checkpoints manned by armed groups at entrances to the eastern town of Slovyansk.
In other incidents on Thursday, Ukrainian Interior Minister Arsen Avakov wrote on Facebook that police had cleared the city hall in Mariupol and that it "has been freed to resume work." Separatist forces confirmed the loss of the city hall.
Warning from Kremlin
Clashes were also reported by the defense ministry in the eastern town of Artemivsk, 40 kilometers (25 miles) southeast of Slovyansk, where authorities repelled an attack on an army base.
The defense ministry said in a statement that nearly 100 separatists "opened fire with automatic weapons, machine guns and used grenades" in the attack on the military base.
Russian President Vladimir Putin said on Thursday that the deployment of military in eastern Ukraine by the authorities in Kyiv was a crime against its own people that will "have consequences."
"If Kyiv really began to use the army against the country's population... that is a very serious crime against its own people," Putin was quoted as saying by Russian news agencies.
"That is simply a punitive measure that will without question have consequences... including for our inter-governmental relations," he said, without specifying the nature of consequences.
On Tuesday, the Russian Foreign Ministry insisted that Ukraine withdraw its troops from parts of the southeast, while Foreign Minister Sergey Lavrov said Russia would respond if its interests in Ukraine were attacked.
rc/pfd (AFP, AP, dpa, Reuters)