Alexander Zakharchenko, a native of mostly Russian-speaking eastern Ukraine, took over late Thursday as prime minister of the self-proclaimed Donetsk People's Republic, which has declared independence from the central government in Kiev.
He succeeded Alexander Borodai, a Moscow political consultant who reportedly played a role in Russia's annexation of Crimea in March before moving into eastern Ukraine. Borodai has worked for a nationalist tycoon with alleged connections to the Kremlin.
Ukraine's eastern regions have strong ties to Russia, and much of its population was alarmed when a new pro-Western government came to power in Kiev with support from Ukrainian nationalists. The change of government was the result of months of street protests that ousted the pro-Moscow president in February.
In another sign that the rebellion may be losing steam, several other rebel leaders with links to Russia have quietly left the region in the past few weeks.
The Russian commanders "are fleeing like rats," said Andrei, a 27-year-old rebel in Donetsk. Like other locals who have joined the separatist cause, he gave only his first name out of fear of retribution either from the rebel leadership for speaking freely or from the Ukrainian authorities for taking up arms.
"We had hoped for help from Moscow, we had expected Russian troops, but Russia betrayed us," Andrei said. "Many fighters are beginning to think about their future and also are escaping to Russia."
Oleg, a 34-year-old member of a different rebel battalion, said his unit is running out of food, clothes and medicine.
"But we are ready to fight to the end and to die," he said. "Russia left us here to die and we are ready. They simply used us and abandoned us."
The new leader of the insurgency vowed to continue the fight but refrained from urging Moscow to send troops, a call issued by many rebel leaders in the past.
"Only moral support," Zakharchenko said Friday when asked what assistance the rebels expect from Vladimir Putin's government.
The Russian president has faced a storm of criticism from nationalist quarters at home for not sending the Russian army into Ukraine.
Another Moscow resident high up in the rebel hierarchy, Igor Girkin, a former Russian special services officer better known by his assumed name of Strelkov, has become an iconic figure in Russian nationalist circles. Some speak of him as a possible future leader of Russia, a depiction certain to irk Putin.
Ukraine and the West have accused Moscow of beefing up its military on the border, dispatching what NATO estimates is 20,000 troops to the border of Ukraine. The deployment has fueled fears of a Russian invasion under the guise of restoring stability to eastern Ukraine.
The Russian Defense Ministry announced late Friday that it has wrapped up military exercises in southern Russia that the U.S. had decried as a provocative step. The exercises involving fighter jets and bombers were held this week in the Astrakhan region, about 1,000 kilometers (600 miles) from Donetsk.
Speaking Friday at a U.N. Security Council meeting, U.S. Ambassador Samantha Power warned Russia that any further intervention in Ukraine, including under the pretense of delivering humanitarian aid, "would be completely unacceptable and deeply alarming, and it would be viewed as an invasion of Ukraine."
The Russian government has denied Western accusations of backing the Ukrainian mutiny with weapons and soldiers. It also has dismissed Western suspicions that it gave the rebels the surface-to-air missiles used to shoot down a Malaysia Airlines passenger jet over rebel-held territory on July 17, killing all 298 people on board. The rebels have publicly denied shooting down the plane, but one rebel leader told The Associated Press on condition of anonymity that the rebels were involved in the downing.
Ukrainian troops routed the insurgents from smaller towns in the region earlier this month and have now encircled Donetsk, where fighting has crept closer to the city center. An estimated 300,000 of the city's 1 million residents have fled.
The Donetsk city council said four apartment buildings in the city were damaged by artillery barrages overnight, killing at least three civilians and wounding 10 others. Shocked residents gathered at the site in the morning, with some leaving flowers on the pavement to commemorate the victims.
"Nina, my godmother, was blown into pieces right in front of the apartment. They only were able to identify her by her dressing gown," 55-year-old Yevgeny Isayev said as he pointed to a crater next to the building's entrance.
Another resident, Marina Barsuk, 53, said the shelling came a few days after rebels had positioned a Grad multiple-rocket launcher near the apartment building and fired at Ukrainian positions. She and other residents believed the latest shelling came from Ukrainian government troops.
The government has adamantly denied, however, that its forces are shelling populated areas.
"We are not shooting on Donetsk, we are liberating it," Andriy Lysenko, a spokesman for Ukraine's National Security and Defense Council, said Friday. "The residential areas are being shot at by the terrorists from their positions."
Zakharchenko said the shelling has swelled the rebel ranks, with more than 700 men showing up to volunteer in recent days. He also said his forces have seized 18 Grad systems from Ukrainian troops.
His statements could not be independently confirmed. The Ukrainian and Russian armies both use the Soviet-made Grad launchers and now the rebels do too. The Grads fire unguided rockets up to 20 kilometers (12 miles) and their accuracy is very poor, making collateral damage from the shelling of populated areas almost inevitable.