Pro-Russian rebels shot down a Ukrainian military plane carrying 49 soldiers and personnel in Luhansk late Friday.

The Ilyushin-76 aircraft carrying troops and military equipment was fired upon as it approached an airport in the eastern Ukrainian city of Luhansk, media reports said Saturday, citing military sources. The attack on the plane comes a week after separatist rebels attacked Ukrainian troops guarding the Luhansk International Airport, which was under the control of government forces. The attack is being referred to as one of the deadliest attacks in the recent Ukraine crisis.

The incident occurred just a few hours after the government waged an operation against the rebels in Mariupol, in eastern Ukraine. A statement from Ukraine’s defense ministry called the rebels “terrorists” who had "cynically and treacherously" fired on the plane as it was landing at the Luhansk airport, the BBC reported.

Although the airport in Luhansk is controlled by government forces, the rest of city has been taken over by the rebels, who want to secede from Ukraine and join Russia.

Ukraine officials have repeatedly claimed that Russia has been supporting the pro-Moscow rebels but Russia has denied the accusations. The Kiev administration's "anti-terrorist operation," which was launched two months ago, has killed more than 270 people, according to the BBC.

Ukraine’s government on Thursday claimed Russia allowed three tanks to enter the country. Ukraine's claims were substantiated Friday by the U.S., which said that it expected Russia to deny the accusations by insisting that the tanks were taken by Ukrainian forces.

“In the last three days, a convoy of three T-64 tanks, several BM-21 or Grad multiple rocket launchers, and other military vehicles crossed from Russia into Ukraine near the Ukrainian town of Snizhne. This is unacceptable,” Marie Harf, deputy spokesperson for the State Department, said in a statement Friday, adding: “Russia will claim these tanks were taken from Ukrainian forces, but no Ukrainian tank units have been operating in that area.”

Harf added that Ukrainian and Russian negotiators are scheduled to meet in Kiev over the weekend to discuss plans to help de-escalate the tension in the region.