Increasing analysis suggests Russian air defenses might have downed Azerbaijan Airlines flight J2-8243, which crashed in a ball of fire near Aktau,Kazakhstan on Wednesday morning, killing 38 of 67 passengers and crew.

Azerbaijani President Ilham Aliyev has launched a criminal probe to uncover the reasons behind the plane crash.

Aviation experts said Thursday that Russian air defense fire was likely responsible for the Azerbaijani plane crash the day before that killed 38 people and left all 29 survivors injured.

National flags were lowered across Azerbaijan, traffic across the country stopped at noon, and signals were sounded from ships and trains as the country observed a nationwide moment of silence.

Azerbaijan is observing a nationwide day of mourning for the victims of the air crash that killed 38 people and left all 29 survivors injured as speculation mounted about a possible cause of the crash

Azerbaijani and US officials believe a Russian surface-to-air missile caused the deadly crash of an Azerbaijani passenger jet, media reports and a US official said Thursday, as the Kremlin cautioned against “hypotheses” over the disaster.

Thursday is an official day of mourning in Azerbaijan as an investigation is underway to determine what caused an airplane carrying 67 passengers to crash on Christmas Day in Kazakhstan, killing 38 and leaving at least 29 survivors.