Ukraine on Sunday released footage it said showed its troops reaching the border with Russia and re-installing a blue and yellow border post.
The location wasn't specified, but some reports suggested the footage may have been filmed in the Kharkiv region.
The video's release came as Ukraine said it held off Russian offensives in the east, with Western military officials saying that Moscow's campaign there had slowed to a snail's pace.
The Ukrainian military said it held off a renewed offensive in the Dontesk area of the Donbas.
Russian troops also tried to advance near the eastern city of Izyum, but Ukrainian forces stopped them, the governor of Ukraine’s Kharkiv region reported.
Ukraine’s most experienced and best-equipped soldiers are based in eastern Ukraine, where they have fought Moscow-backed separatists for eight years.
Getting a full picture of the unfolding battle in the east has been difficult because airstrikes and artillery barrages have made it extremely dangerous for reporters to move around.
Both Ukraine and the Moscow-backed rebels fighting in the east also have introduced tight restrictions on reporting from the combat zone.