A column of armored vehicles and artillery pieces including three tanks has crossed the Russia-Ukraine border near the Ukrainian city of Snizhne into the country’s eastern rebel-held territory, Ukraine’s Interior Minister told reporters in Kiev today.

The statement from Arsen Avakov is the first admission by Ukrainian authorities that its border with Russia on the edge of the two rebel republics in Luhansk and Donetsk is beyond its full control.

Reuters news agency reported that its correspondents had spotted three tanks in the vicinity of the town, which is 65 miles from the border.

Avakov further added that Ukrainian forces had destroyed part of the column, and that a fight was underway near Gorlovka, but did not give any further details. However, a rebel spokesperson from Gorlovka told VICE News that there was no fighting in the immediate vicinity, but that clashes were underway near Torez — a village between Luhansk and Donetsk.

Unverified film footage that briefly appeared on YouTube and was shot from an apartment block window seemed to show one tank racing through the streets of Snizhne.

Russian authorities that recently pledged to tighten border controls have rejected Avakov's statement regarding the recent movement of military vehicles across the border as "another fake piece of information."

The incident comes just one day after the Advisor to the Interior Minister Anton Herashchenko told Ukraine’s Channel 5 that the search for necessary means and methods of closing the country’s border with Russia were underway. The option of mining the area had not been ruled out, he added.

The area around where the tanks were spotted has become a hotspot for fighting and detentions recently, sparking rumors that the region is becoming the new stronghold for rebels seeking to move reinforcements into the country's east across the nearby Russian border.

Russia has denied assisting the rebels in their struggle, but both fighters and arms appear to have been able to flow relatively freely into Ukraine in recent weeks since the rebels began a program of border station seizures.

Vladyslav Bagryntsev, the deputy commander of a Luhansk Cossack Unit, confirmed to VICE News that the large swathes of the region’s border with Russia were under the control of the rebel-aligned Cossack forces operating in the region.

“We hold eight border posts,” he told VICE News.

Vadim Zadunaiskiy, a history professor at Donetsk National University, told VICE News that the Cossack paramilitary groups operating in Luhansk and neighboring Donetsk have strong ties with their Russian counterparts.

The militia groups operating in eastern Ukraine have appeared on the streets increasingly well armed, with numerous armored personnel carriers and a large stock of automatic weaponry and rocket-propelled grenade launchers. However, it is unclear whether the equipment was brought across the border or seized by the rebels after clashes with Ukrainian security forces.

Rebel leaders on EU and US sanctions and the Ukrainian government’s wanted list have also been able to travel with ease across the country’s border with Russia.

On Wednesday Denis Pushilin, the self-styled chairman of the Donetsk People's Republic, was spotted meeting Russian nationalist leader Vladimir Zhirinovsky in Moscow.

It is unclear whether the tanks originated in Russia. They could have also come from Crimea, or been seized by the rebels during clashes with the Ukrainian army.

Meanwhile in a separate incident in Donetsk city around 9PM Thursday night, the region’s administrative center, a loud explosion echoed through the streets as a car bomb exploded outside the rebels headquarters, which is under the guard of heavily armed rebels. Nervous gunfire was heard in the moments following the boom. The vehicle reportedly belonged to DPR leader Pushilin, who was not in it at the time.

"The car explosion killed two persons, one of them was my aide and the other was a security guard. The driver and people who were passing by got injured. I know that a third person has died, too. We have yet to identify him. My aide died from lethal injuries this morning on the operating table," Pushilin told Interfax.

On Thursday night a spokesperson at the Donetsk Governor's office told VICE News that several people were injured in the explosion, some seriously.

Rumors of rifts between the rebel leaders have been rife in recent weeks, but no one has yet claimed responsibility for the attack.

This is the second seeming attempt on Pushilin’s life inside one week. Last Saturday the assistant of the DPR's self-styled leader, Maksym Petrukhin, was shot dead in the city center.