Kazakh investigators are still analysing the Azerbaijan Airlines Embraer 190 crash at Aktau a year ago, stating that the exact origin of suspected missile fragments has not been determined.

The aircraft aborted an attempt to land at Grozny on 25 December last year, but was crippled by two explosions and – with substantial flight-control difficulty – diverted to Aktau where it crashed while trying to make an emergency landing.

In an interim statement on the anniversary of the event, the Kazakh ministry of transport’s accident investigation department states that “comprehensive” ballistic, explosive and traceological analysis has been conducted on “foreign objects” identified in the wreckage.

It says preliminary assessment indicates the damage to the jet was caused by “elements” from a missile, “but it was not possible to establish their origin”.

There were “no traces” of explosive substances, it adds, but examination of damage to hydraulics indicates “metal rupture resulting from contact with hard objects” and may have been caused by foreign metallic fragments composed of steel-based material.

No evidence of explosion from three oxygen cylinders was found. The E190’s crew had initially suspected an oxygen tank explosion.

While the interim statement does not confirm the origin of the fragments, Russian president Vladimir Putin acknowledged in October that failures in the country’s air-defence system contributed to the event.

Putin indicated that the E190 was probably hit by debris from two surface-to-air missiles – fired in response to the presence of Ukrainian drones – although they had not hit the aircraft directly.

The inquiry commission is still compiling a final report into the event.

Investigators are awaiting the results of examination of the E190’s central maintenance computer, data from which has proven difficult to obtain owing to thermal damage. The inquiry says it has been co-ordinating with US representatives over the possible extraction of data from the memory card.

The inquiry is also analysing GPS avionics data and the finding of a risk analysis on flights near conflict zones.

It states that the investigation is taking a “balanced approach”, adding: “All conclusions will be objective and based solely on facts.”

Thirty-eight occupants, including three crew members, did not survive the crash at Aktau. Another 29 sustained various level of injury.