At the end of September, in separatist-controlled eastern Ukraine, the Organization for Security and Co-operation in Europe located a Russian-made rocket launch system that had never been exported to the Ukrainian military.

The system, a 220mm TOS-1 Buratino thermobaric multiple rocket launch system, is one of the most blatant pieces of evidence to surface so far showing Russia’s involvement in the almost two-year-long war. And now the UK wants Russia to answer for its presence in the war-torn east.

“The Buratino is produced in Russia and has never been exported to Ukraine,” the UK’s Delegation to the OSCE said in a tweeted statement Wednesday. “We are requesting the delegation of the Russian Federation to explain the presence of the TOS-1 Buratino in this training area.”

Russia has repeatedly denied claims of sending troops or equipment into Ukraine.

The OSCE, which provides almost daily updates on the situation in the country, identified the Buratino on Sep. 25 parked in a training area near the Ukrainian city of Luhansk. A few days later it was gone.

The Buratino is a mobile piece of rocket artillery mounted on a tank chassis that can blanket large target areas with fuel-loaded rockets. The rockets saturate the area before igniting, giving the impression that the Buratino is a type of “flamethrower.”

While other multiple-rocket launch systems, such as the BM-21 Grad and BM-30 Smerch, have been used in Ukraine, the TOS-1 is recognized as a significantly more devastating weapon.

In the past, Russia has sold the system to Iraq and at least one has recently been spotted in Syria, helping with the current Russian-backed offensive in the west of the country.

More than 7,000 people have died since the conflict in Ukraine began in 2014. Wednesday marked the first death caused by hostile fire in a month when a Ukrainian soldier was killed by small arms fire. Aside from the occasional cease-fire violation, a shaky truce has held between the Ukrainian military and Russian-back separatists since early September.