A spokesman for Ukraine's national security council says "dozens" of civilians have been killed in a rebel attack on a convoy of people trying to flee war-torn eastern Ukraine.
"Many people were killed, among them women and children," Colonel Andriy Lysenko told reporters Monday, adding that he is unable to provide exact figures, but that dozens died, including children.
The separatist rebels fighting Ukrainian troops have not yet commented on the government's statement.
The barrage took place between the towns of Khryashchuvate and Novosvitlivka, which lie on the main road leading to Russia from the besieged rebel-held city of Luhansk.
That road is likely the one that a convoy of Russian humanitarian aid would take if Ukraine allows it into the country. The hard-hit city of Luhansk is said to be where the aid is most needed.
Fighting across eastern Ukraine has forced nearly 344,000 people to flee their homes, according to UN figures released Friday. The UN says about 155,800 have left for other places inside Ukraine while 188,000 more have crossed into Russia.
The flow of refugees only seems to be growing. The UN Office for the Coordination of Humanitarian Affairs said more than 22,000 people fled Donetsk last week compared to 6,200 the week before.
City officials have released even higher numbers. Donetsk, the largest Ukrainian city still under rebel control, has seen at least 300,000 of its pre-war population of 1 million leave their homes, while Luhansk has only 250,000 of its 420,000 people left, local authorities have said.
Residents in Luhansk have had no running water, power or phone connections for 16 days. Basic foods are in short supply, leading to long lines outside shops and markets. The city hall said Monday that fighting continues in and around of the city.
The International Committee of the Red Cross, which is to take responsibility for the Russian aid convoy when it enters Ukraine, has demanded security guarantees from all sides, including the rebels, for the mission into eastern Ukraine. As of Monday, there was no indication that the guarantees had been given.
Russia's foreign minister said he expects the Russian humanitarian aid mission for eastern Ukraine to enter the country in the near future.
Speaking Monday at news conference in Berlin, where he met a day earlier with his counterparts from Ukraine, France and Germany, Russian Foreign Minister Sergei Lavrov said all questions regarding the mission had been answered and that an agreement had been reached with Ukraine and the ICRC.
It was not clear if Lavrov was referring to the security guarantees.
The humanitarian aid convoy of more than 200 trucks from Russia has been watched with suspicion by Ukraine and Western countries, especially since Ukrainian forces have been winning back significant territory from the rebels in the last few weeks. They suggest it could be used by Russia to send help into the separatists — or to delay the government's advances with a timely cease-fire.
The fighting in eastern Ukraine began in mid-April, a month after Russia annexed Ukraine's southern peninsula of Crimea.