Evidence suggests a deadly explosion at a busy market in the eastern Ukrainian city of Kostiantynivka this month was caused by an errant missile fired by Ukraine, the New York Times reported on Tuesday.

Ukraine has said the Sept. 6 blast, which killed at least 16 people, was caused by a Russian missile.

“Evidence collected and analyzed by The New York Times, including missile fragments, satellite imagery, witness accounts and social media posts, strongly suggests the catastrophic strike was the result of an errant Ukrainian air defense missile fired by a Buk launch system,” the newspaper reported.

It quoted air defence experts as saying missiles such as the one that hit Kostiantynivka can go off course for a variety of reasons, including an electronic malfunction or having a guidance fin that is damaged or sheared off during launch.

It said security camera footage showed the missile flew into Kostiantynivka from the direction of Ukrainian-held territory, not from behind Russian lines.

The New York Times also cited evidence showing that minutes before the strike, the Ukrainian military had launched two surface-to-air missiles towards the Russian front line from the town of Druzhkivka, 10 miles (16 km) northwest of Kostiantynivka.

It quoted two witnesses who said they had seen the missiles being fired from Druzhkivka in the direction of the Russian front line around the time of the strike. One was quoted as saying the missiles went in the direction of Kostiantynivka.

The newspaper said measurements of holes caused by the explosion and fragments found at the scene were consistent with the 9M38 missile, which is fired by the mobile Buk anti-aircraft vehicle.

The Buk system is used both by Ukraine and Russia.

Reuters could not independently verify the report. A Ukrainian presidential aide did not immediately respond to requests by Reuters for comment.

The New York Times quoted a spokesperson for Ukraine’s armed forces as saying the country’s security service was investigating the incident, and under national law could not comment further.

A spokesperson for Ukraine’s military command referred Reuters to that comment cited in the New York Times story.

Russia responded by saying that Ukraine was responsible for the explosion.

Russian Foreign Ministry spokeswoman Maria Zakharova said Ukraine had fired a 9M38 missile from a Buk surface-to-air missile system which struck the city.

“Even if it was done unintentionally, it is obvious to everyone: the complete demilitarisation of the Kyiv regime is not just a requirement, but a vital necessity,” Zakharova said.