Ukraine’s control over its borders seemed tenuous at best. On Wednesday evening, armed men in camouflage, some with bandannas tied on their heads, strode confidently around the small border post area here, which is little more than a small collection of buildings, a stop sign and a security gate. The Ukrainian flag had been taken down and the signature green trucks of the Ukrainian border guards were gone. No Ukrainian military uniforms could be seen.

“These are our guys,” said Alexei, a taxi driver who supports the rebels and noticed the change of guard in the late afternoon. “The entrance is open now.”

In the city of Luhansk, the capital of Ukraine’s easternmost region, a lone military base at the airport was the remaining element of control by the central government. A visit by journalists on Wednesday showed a small contingent of police and army officers who were huddled behind concrete guard posts and appeared on edge.

Bases seemed to fall one after another. On Tuesday night, the rebels overran a base for Ukrainian internal security forces in Luhansk, with gunfire rattling in the center of the city for hours. The police forces inside were ordered to remove their uniforms, and on Wednesday morning they lay in a messy pile inside the base, whose perimeter was smeared with blood in three places. The Associated Press cited officials as saying six militants were killed and three Ukrainian servicemen were injured in the fighting.

“It’s chaos,” said a massage therapist who identified herself only as Zhanna, and who lives in an apartment building, the roof of which rebels used to fire on the border guard base. She pointed to empty boxes of ammunition in her building’s stairwell. “These are bandits, plain and simple,” she said of the rebels.

She expressed pity for the border guards, whom she said were mostly young men from the area trying to feed their families.