Rebels in eastern Ukraine appeared to be successfully closing in on the government-held airport in Donetsk Wednesday, a strategic victory for the pro-Russian separatists.

At least 10 people were killed as residential areas near the airport were caught in the crossfire, further undermining a shaky truce that was imposed last month and has been riddled by violations since.

Ukraine's National Security and Defense Council spokesman Andriy Lysenko told journalists in Kiev that the airport was still under control of government troops who were "brilliantly carrying out their duty" and holding ground there.

However, rebel leader Alexander Zakharchenko was quoted by Interfax news agency as saying that the rebels control 90 percent of the airport, which has been the focus of the worst fighting in the region for weeks.

"In two, or maximum three, days the Donetsk airport will come under our control," he said.

While it was impossible to get within close range of the airport because of the ongoing fighting, an AP reporter in Donetsk saw that artillery fire hitting the airport was coming from government-held positions outside the city — an indication that the airport may no longer be under Kiev's control.

The reporter also saw the bodies of three people killed after a shell exploded in a school courtyard in a residential neighborhood near the airport. The city council of Donetsk said that in total four people had died, and that about 70 schoolchildren were in the school at the time but that all those killed were adults.

Soon after the school was hit, another shell fell on a bus stop nearby. The AP saw two people who had been killed at the bus stop as well as another person on the crosswalk nearby. A minibus that was also hit was still burning hours later — though the AP was unable to confirm how many people were in the bus. The Donetsk city council said the number of killed at the bus stop was six, and that several people were wounded.

In Moscow, Russian Foreign Minister Sergey Lavrov continued to call on the West to look into allegations that there are mass graves in eastern Ukraine of those killed by Ukrainian troops.

"It's a terrible tragedy. It's an obvious war crime," he was quoted as saying by Russian news agencies. "We count on Western capitals not being silent about these facts."