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Picture taken in 1917 shows Nicholas II, Czar of Russia, and his family, in one of the latest pictures taken before the Revolution. From Left: Princesses Olga and Maria, Nicholas II, Czarine Alexandra, Princess Anatasia, Czarevitch Alexei and Princess Tatiana.

DNA tests carried out by a U.S. laboratory prove that bone fragments exhumed last year belong to two children of Czar Nicholas II, putting to rest questions about what happened to Russia's last royal family, a regional governor said Wednesday.

Bone fragments dug up near the Ural Mountains city of Yekaterinburg are indeed those of Crown Prince Alexei and his sister, Maria, whose remains had been missing since the family was murdered in 1918 as Russia descended into civil war, said Eduard Rossel, governor of the Sverdlovsk region.

"We have now found the entire family," he told reporters in Yekaterinburg, 1500 kilometres east of Moscow.

The confirmation could bring the tortured history of the Russian imperial family closer to closure and end royal supporters' persistent hopes that members of the czar's immediate family survived the massacre.

Nicholas II abdicated in 1917 as revolutionary fervour swept Russia, and he and his family were detained. The czar; his wife, Alexandra, and their son and four daughters were fatally shot on July 17, 1918, in a basement room of the merchant's house where they were being held in Yekaterinburg

The remains of Nicholas, Alexandra and three of their daughters were unearthed in Yekaterinburg in 1991 as the Soviet Union was collapsing. After genetic tests convinced forensics experts of their authenticity, they were buried in 1998 in a cathedral in the imperial capital of St. Petersburg.

The Russian Orthodox Church canonized Nicholas and his family in 2000, even as it expressed doubts that the remains were indeed those of the czar's family.

The remains of Alexei and Maria, however, had never been located, leading to decades of speculation that perhaps one or both had survived.

Last summer, researchers dug up the bone shards near Yekaterinburg and enlisted Russian and U.S. laboratories to conduct DNA tests.

"The main genetic laboratory in the United States has concluded its work with a full confirmation of our own laboratories' work," Mr. Rossel told reporters. "This has confirmed that indeed it is the children.

It was unclear which laboratory Mr. Rossel was referring to but a genetic research team working at the University of Massachusetts Medical School has been involved in the process.

The press service for Russian Orthodox Church said no one could comment on the discovery.