Rockets hit Tuesday a government-controlled town in Ukraine about 50 miles from the front line, where government troops are nearly surrounded by rebel forces. At least six people were killed and 21 wounded, according to Agence France-Presse. Ukrainian President Petro Poroshenko said the rockets were part of a state-of-the-art Russian system that only entered service last year and have not yet been exported outside of Russia, but that claim has not been independently verified.

There were two attacks, according to Poroshenko. The first targeted the government’s main command center for the fighting in the east and the other “was carried out on residential areas of Kramatorsk,” he said, according to Reuters. There at least one civilian was killed and six were wounded. The local government said the attacks came from Horlivka, a rebel-controlled town about 50 km (30 miles) from Kramatorsk.

Rebels denied they were responsible for the attack. A representative said “there were no strikes by us from any kind of weapon in the direction of Kramatorsk,” according to Reuters.

Rebel forces also pounded government positions Tuesday in Debaltseve, a nearby city with a critical railway hub that connects the two rebel “capitals” of Donetsk and Luhansk. The town has been a center of fighting for the last two weeks. Rebels said they cut off the Ukrainian army’s last major supply route.

Rocket and artillery attacks have accounted for around 60 percent of government casualties and most civilian deaths in the east since the conflict began in the spring of 2014. Both sides have primarily used the MB-21 Grad rocket, a truck-mounted Soviet system that entered service in the early 1960s.

Dmytro Kuleba of the Ukrainian Foreign Ministry said the attacks were the work of Russia’s new Tornado system. If true, it would be the first instance of the Tornado being used in Ukraine.