Kiev, Ukraine (CNN) -- Civilians, including women and children, have been killed in an attack on a caravan of refugees in Ukraine's eastern Luhansk region, the Ukrainian military said Monday.
The civilians were trying to escape fighting between pro-Russian rebels and the Ukrainian military but were not in an established humanitarian safety corridor when they came under fire, a military representative said.
The civilians were being escorted by the Ukrainian military from the towns of Khryaschuvate and Novosvitlivka when they were attacked at 9:40 a.m. local time (2:40 a.m. ET), the Kiev-recognized Luhansk Regional Government said.
A government representative confirmed that there had been "heavy gunfire" in the area and that the victims had been unable to call for help as mobile phone towers were down.
Ukrainian Col. Andriy Lysenko told CNN that "terrorists" had attacked the caravan with guns from Russia.
Lysenko later told media that preliminary information indicated that the attack had been an ambush. The caravan was almost destroyed, and tens of people were killed, he said. Lysenko said that people had been registering to leave with the caravan for several days before the attack.
Ukraine's state information agency reported that Grad launchers and mortars had been fired at those trying to leave the war zone.
There had been 25 battles in the past 24 hours, with government forces regaining part of the city of Luhansk, Lysenko said. "Luhansk is almost fully encircled, and the operation to free it is going on right now," he said.
The rebels had used Uragan rocket launchers for the first time, Lysenko said.
Ukraine on Sunday reported gains against the rebels, saying the army had entered Donetsk and raised the Ukrainian flag in front of the district's police offices. Ukrainian forces also regained control of the strategic town of Yasynuvata in Donetsk in the southeastern part of the country, according to the official Twitter account of President Petro Poroshenko.
On Monday, Russian state-run news agency RIA Novosti reported that the self-styled Donetsk People's Republic had announced the death penalty would be introduced "for the gravest crimes."
Once the war ended, the group would step "on the path of humanization of the criminal law," RIA Novosti quoted a DPR minister as saying, after a meeting of its council Sunday.
Humanitarian agencies say thousands of people in the region don't have access to water, electricity and proper medical aid.
Ongoing fighting downed power lines and stopped Donetsk city's water treatment plant from working Sunday, the City Council said. The Donetsk City Council announced on its website that the water supply would be cut off starting at 9 p.m. local time (2 p.m. ET). In a new statement Monday, it said the supply remained disrupted, with fighting hindering repairs.
Ukrainian officials acknowledged Sunday that a convoy of more than 260 Russian vehicles on the border is, in fact, carrying humanitarian aid, a statement on the Ukrainian Cabinet website said.
Ukraine received an inventory of the supplies Saturday, which was signed by the head of the regional International Committee of the Red Cross (ICRC) delegation to Russia.
But Col. Lysenko said Monday that failure to reach an agreement on safety with the ICRC had prevented a detailed inspection.
The convoy initially sparked fears that Russia was trying to use a humanitarian convoy as a cover for sending in more aid and weapons for pro-Russian rebels in eastern Ukraine, which Russia and the rebels denied.
The ongoing fighting -- sparked last year by a political crisis over whether Ukraine would seek closer ties with Europe or Russia -- has left more than 2,000 people dead and just under 5,000 wounded in eastern Ukraine since mid-April, according to estimates from U.N. officials.
Progress reported in cease-fire talks
The foreign ministers of Ukraine, Russia, Germany and France met in Berlin on Sunday to discuss the crisis in Ukraine.
"We discussed the question of how we can find ways to reach an urgently needed cease-fire in eastern Ukraine," German Foreign Minister Frank-Walter Steinmeier said. "We discussed the question of how we can improve and optimize controls at the Russian-Ukrainian border."
Steinmeir said progress had been made in certain areas and the parties were looking at further talks.
Russia's Foreign Ministry released a statement saying the talks focused on "the earliest possible termination of the hostilities, border control, humanitarian aid delivery to southeastern Ukraine, and creating the conditions for the earliest beginning of the process of political settlement."
"Some progress was made on all these issues," it said.
The United States and the European Union have applied steadily increasing sanctions against Russian officials, banks and other interests since March, when Russia annexed the Black Sea Ukrainian peninsula of Crimea. Russia's move came a month after Ukraine's parliament ousted pro-Moscow President Viktor Yanukovych.
Yanukovych left office after violent protests against his government in the capital, Kiev. Those protests were motivated in part by his decision to back out of a trade deal with the European Union in favor of closer ties with Russia.
CNN's Will Ripley and Victoria Butenko reported from Kiev.