MOSCOW-- Russian officials say they have closed three major border crossings in the wake of heavy fighting in Ukraine.
Russian news agencies on Friday quoted Vasily Malayev, spokesman for the Federal Security Service in the Rostov region, as saying that three crossings east of Donetsk were temporarily closed late Thursday night because of fighting on the other side.
Ukraine says it regained control of one crossing which had been controlled by rebels.
Pro-Russian insurgents in eastern Ukraine have declared independence and have been fighting Ukrainian government troops for more than three months. Government forces have been advancing in the recent days, pushing the insurgents closer to the Russian border.
Malayev told RIA Novosti on Friday customs staffers had been evacuated from the border crossing while border guards remained at their positions.
Deep strains emerged Thursday in the ranks of Ukraine's pro-Moscow insurgents as dozens turned in their weapons in disgust at Russian inaction and bickering broke out between rebel factions.
In the past two weeks, Ukrainian government troops have halved the amount of territory held by the rebels and have grown better equipped and more confident by the day. Once fearful of losing further pieces of Ukraine to Russia, they have shifted their strategy to containing the insurgents, whose pleas to join Russia have been ignored by President Vladimir Putin.
Pushed back into Ukraine's eastern industrial city of Donetsk, the pro-Russia militias appear to be focusing their efforts now on hit-and-run operations, bombing transportation links and bracing for more assaults from government forces.
Signs of a rift within the rebellion became evident Thursday when the head of the influential Vostok battalion announced he would not submit to the authority of the military leader of the separatist Donetsk People's Republic, Igor Girkin.
Girkin, a Russian better known by his assumed name Strelkov, has attained hero status among supporters of the insurgency. Ukrainian authorities have identified him as a former Russian military intelligence agent active in taking over Crimea before Russia annexed it in March.
Yet he has also been criticized by some for leading the rebel withdrawal last weekend from the eastern city of Slavyansk, 70 miles north of Donetsk, reportedly to protect civilian lives
Vostok commander Alexander Khodakovsky alluded to that.
"There cannot be a single leader giving orders," he declared. "Because if Strelkov suddenly decides what he wants is - in the interests of protecting the lives of Donetsk citizens and the lives of militiamen - to abandon Donetsk, then we will not follow his orders."
Khodakovsky was speaking in Makiivka, a town just outside Donetsk, where his men relocated after a reported falling-out with Strelkov.
The ill will also appears to stem from a feeling among the rebels that Russia has done too little to help them.
"Strelkov is a military officer of non-local domicile, while we are locals and will not, therefore, allow the people of Donetsk to remain without our support and protection," Khodakovsky said.
Strelkov could go back to Russia whenever he wanted, he noted.
Ukraine says Moscow is arming and supporting the rebels, charges it has denied.
In another sign of deteriorating morale among the rebels, several dozen militia fighters garrisoned in a university dorm in Donetsk abandoned their weapons and fatigues in their rooms Thursday.
"Russia abandoned us. The leadership is bickering. They promise us money but don't pay it. What's the point of fighting?" said 29-year old Oleg, a former miner.
Oleg, who declined to give his surname for fear of being punished for desertion, said he had served in the militia for a month and planned to go home to Makiivka.
Strelkov has admitted substantial difficulties enlisting the support of the locals in eastern Ukraine.
"In truth, the number of volunteers for the several million-strong population of Donbass, for a mining region where people are used to dangerous and difficult work, has been somewhat low," he told a rebel-run TV station this week. "It is very difficult to protect this territory with the forces at our disposal."
At a news conference, the prime minister of the Donetsk People's Republic dismissed talk of infighting.
"These are lies and disinformation. There are no disagreements. We are now organizing our joint work," Alexander Boroday said.
He said 70,000 Donetsk residents have been evacuated from the city and more will follow. He did not elaborate.
While rebels hold Donetsk, the city's international airport, which has been closed since early May, remains in government hands. Militia forces mounted an artillery assault on the terminal Thursday.
"Our aim was not to capture the airport. The enemy sustained serious casualties," Strelkov said.
His claim could not be independently verified.
Rebels regularly conduct lightning attacks on checkpoints, and earlier this week they blew up three bridges leading into Donetsk to hinder the movement of Ukrainian troops.
While waging what increasingly resembles guerrilla warfare, Strelkov has said he wants to transform the rebels into a regular standing army with a unified command. The rebel leadership also said this week it will pay its soldiers monthly salaries of $500 to $700.
The plans to create a professional army also reflect the inability to recruit more volunteers.
"I know many of them from school. I support them, but I am not going to fight," said 39-year laborer Artyom Yermolyuk. "What awaits them when this is all over and the Ukrainian authorities are here?"