Kyiv is accusing Russia of building up forces on its border with Ukraine and says that separatists backed by "Russian mercenaries" are firing on Ukrainian border guards in an attempt to bring armored vehicles into the country.
Ukrainian National and Security Council spokesman Andriy Lysenko told journalists that the clashes took place in the early hours of July 14 near the border settlement of Dyakove.
He said the events "show that the Russian side has embarked on a course of escalation of the conflict in the Donbas."
In other charges of increasing Russian involvement, Ukrainian President Petro Poroshenko told a meeting with senior army and security officials in Kyiv on July 14 that "in the past three days a new Russian missile system has been used against the armed forces of Ukraine."
A July 14 statement on the Ukrainian presidential website said that "information has also been confirmed that Russian staff officers are taking part in military operations against Ukrainian forces."
Poroshenko also said there was a need for tactical changes by Ukrainian forces to strengthen the defense of the border and protect people living near it.
Meanwhile, the Ukrainian military said on July 14 that its forces, backed by warplanes, had broken a rebel blockade of the Luhansk airport in eastern Ukraine.
The military said the air strikes inflicted heavy losses on the pro-Russian separatists, including an armored convoy which Kyiv says crossed the border from Russia.
Casualty figures on both sides are difficult to confirm.
Separatists from the self-proclaimed "Luhansk People's Republic" claimed on July 14 to have shot down two Ukrainian combat planes in eastern Ukraine -- one in the area of Lisichansk and the other near the border checkpoint of Izvarino.
Meanwhile, Ukrainian security officials are quoted as saying they have lost contact with an Antonov military transport plane near Luhansk.
Russia on July 14 threatened Ukraine with "irreversible consequences" after a man in the small Russian border town of Donetsk was killed from a shell allegedly fired from Ukraine.
President Vladimir Putin expressed "grave concern" over the incident, according to a Kremlin spokesman.
Kyiv denied its forces had fired across the border, calling such charges "total nonsense."
With reporting by Reuters and AP