ARTEMIVSK, Ukraine — The plight of as many as 8,000 Ukrainian troops trapped in the vicinity of Debaltseve, as well as the prospects for an already fragile truce, look decidedly dimmer on Monday after a Russian television correspondent strolled down what was supposed to be a hotly contested road.

The video on the Russian channel Life News, if reliable, seemed to prove that the road, the only artery of support for the Ukrainian troops, was firmly in the hands of the separatists.

The status of this stretch of potholed asphalt has become a sticking point in the cease-fire and threatens to unravel the deal. The separatists say their control of the road means they have the Ukrainians surrounded. President Petro O. Poroshenko of Ukraine has denied their claim, because conceding the point would force him either to negotiate for the release of the trapped soldiers or resume fighting to extricate them.

A dozen or so soldiers escaped on Sunday, and on Friday a small group reportedly managed to walk out through the fields. Otherwise, nobody has left the town since Thursday.