Ukrainian border guards detained a soldier suspected of being a Russian army officer who was picked up while riding in a military truck packed with ammunition at the Berezove checkpoint, about 28 miles southwest of the militant-held city of Donetsk.

Guards found nearly 200 cases containing grenades and ammunition, including rocket-propelled shells, inside the military truck.

"He (the Russian officer) had no documents. But he admitted that he was a chief of an RAO (rocket-artillery weapons unit). He is responsible for ammunition supply. He said that while delivering the ammunition they had got lost," Oleksandr Tomchyshyn, a border-guards spokesman said. Another man who was detained identified himself as a pro-Russian separatist fighter.

If he is confirmed as a Russian soldier, Ukraine is likely to use the case to bolster its charges that Russia is continuing direct involvement in the 15-month-long conflict and failing to honor a peace agreement worked out in Minsk, Belarus, in February. Meanwhile, Ukraine and Western countries contend that Russia is providing troops and weaponry to pro-Russian rebels in eastern Ukraine.

Since April 2014, at least 6,400 people have been killed in the region while Russia continues to deny such allegations, the Associated Press reports.

A spokesman said the two men may have taken a wrong direction and driven toward Ukrainian forces manning a checkpoint southwest of the rebel-controlled city of Donetsk by mistake.

"We can assume that they took a wrong direction while driving, got lost, and came on our checkpoint," military spokesman Oleksandr Motuzyanuk told a briefing.

More weapons found crossing into the Berezove checkpoint. Screen grab/Ukraine Today The two men wore military uniforms without insignia and carried no identity documents, he said.

In the face of what Kiev and Western governments say is undeniable proof, Moscow denies its regular forces are engaged actively in the conflict on behalf of the separatists.

Though a fragile ceasefire seems to be holding, thousands of people have been killed in the conflict in Ukraine's industrialized Russian-speaking east.

Ukraine is still holding two Russian soldiers who were captured in May and have been charged with terrorism. Russia says the two men had quit their special-forces unit to go to Ukraine on their own.

Here is a video of the truck found at the Berezove checkpoint:

(Writing by Richard Balmforth; Editing by Angus MacSwan)