Monitors from the Organization for Security and Cooperation in Europe (OSCE) at the Gukovo checkpoint in Russia's Rostov region near the border with Ukraine have reportedly vacated the area due to safety concerns.
Russian Federal Security Service (FSB) spokesman Vasily Malayev says the OSCE mission left the site on August 4 amid continuing military operations by Ukrainian government forces against pro-Russian separatists in eastern Ukraine.
Malayev added that more than 400 Ukrainian troops, including some 160 Ukrainian border guards, had entered Russian territory on August 4, after the Russian side allowed them to cross the border at the Gukovo check point.
According to Malayev, the Ukrainian troops will be transferred to the control of the Ukrainian government at the Matveyev-Kurgan checkpoint in the near future.
It was not immediately clear why the Ukrainian soldiers crossed into Russian territory.
But Ukrainian reports said the soldiers fled into Russia to escape artillery barrages being fired at them from Russian territory.