The Azerbaijani Prosecutor General's Office has opened a criminal case into the deliberate murder of two Azerbaijani citizens by Russian law enforcement officers, the BBC reports.

The Azerbaijani side claims that the brothers Ziyaddin and Huseyn Safarov died of post-traumatic shock after receiving bodily injuries. According to the Russian Investigative Committee, one of the detainees died of heart failure.

Russian authorities have announced that they arrested—in Yekaterinburg—suspects in the 2001, 2010, and 2011 murders.

The aforesaid Azerbaijani brothers died during their arrest, and several others were hospitalized.

The bodies of the Safarov brothers were flown to Azerbaijani capital Baku on Monday evening, and they were buried on Tuesday.

Separately, the Yekaterinburg court has arrested another Azerbaijani, Bakir Safarov, in the same case in which the Safarov brothers were arrested.

The reports on the deaths of two people and of mass arrests in Yekaterinburg have led to another escalation of relations between Baku and Moscow.

Russian cultural events have been canceled in Azerbaijan, and two Russian journalists, believed to be Russian Federal Security Service (FSB) agents, have been detained at Russia’s Sputnik Azerbaijan news agency office in Baku. And the Azerbaijani ambassador to Russia, Rahman Mustafayev, was summoned to the Russian foreign ministry.