Russian investigators exhumed the remains of the country's last czar and his wife Wednesday in the hope of confirming the identities of two other sets of remains as belonging to two of their children. 

Czar Nicholas II, his wife Alexandra and their five children were executed by Bolshevik revolutionaries in 1918 as White Army forces closed in on the city of Yekaterinburg, where they were being held captive. The remains of Nicholas, Alexandra, and their daughters Anastasia, Olga and Tatiana were found in a mass grave in the Ural Mountains in 1991, but were not identified through DNA testing for another seven years.

In 2007, remains thought to be those of Alexei, Nicholas's only son and heir, and the couple's other daughter, Maria, were discovered some distance away from where their parents and sisters were found. The Russian government had announced burial plans earlier this month, but the Russian Orthodox Church called for further investigation.

The church has canonized the royal family and deems worshipping false relics to be sacrilege. It does not consider the remains found in 2007 to be authentic, in part because of the distance between the two sets of remains.

Sky News quoted senior Investigator Vladimir Solovyov, who heads the investigating team, as telling Russia's TASS news agency: "The exhumation was done in the presence of representatives of the Russian Orthodox Church. The necessary samples were taken from the remains of Nicholas II and Empress Alexandra Fyodorovna.

"Also, samples for blood [were taken] from the stains on the full-dress uniform of [Czar Nicholas II's grandfather] Emperor Alexander II, who was killed by radical revolutionaries on March 1, 1881."

The remains have now been returned to the crypt of the St Catherine sacrarium in St Peter and Paul's Cathedral in St Petersburg, officials said. Sky reported that the two sets of unidentified remains are being kept at the Russian State Archives until their identity is confirmed. 

The Associated Press contributed to this report.

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