Russian investigators said today new DNA tests conducted at the request of the Orthodox Church had confirmed that the exhumed remains of Nicholas II, the country's murdered last tsar, and his wife, were genuine.

The statement brings closer the possibility that the entire Romanov family -- who were executed by the Bolsheviks in 1918 -- could be laid to rest together with the purported remains of Alexei and Maria, two of the tsar's five children, also interred in St Petersburg with the others for the first time.

The church, which canonised the slain family in 2000, has been pushing for extra proof that the remains of Nicholas, whose Romanov dynasty ruled Russia for 300 years, are bona fide, a precondition for Alexei and Maria to be buried.

It has also asked for more tests to check that the purported remains of the two children, found only in 2007, are genuine.

Forensic experts from Russia's Investigative Committee exhumed the remains of Nicholas and his wife Alexandra in September, taking DNA samples that had not previously been analysed.

Those samples corresponded with earlier findings and showed that the remains were genuine, the committee said in a statement.

"These samples revealed heteroplasmy -- a rare genetic mutation that was present in (earlier) samples of Nicholas II," it said.

Nicholas II, his wife, and their five children were murdered by the Bolsheviks in 1918 along with their servants in the city of Yekaterinburg in the Urals.

The bodies of Nicholas and Alexandra and three of their daughters were reburied in St Petersburg in 1991 and an initial five-year investigation, launched in 1993, confirmed the authenticity of those remains.

The committee said on Wednesday it would conduct further tests to reach a "highly reliable final conclusion." It said last month it also planned to exhume the remains of Tsar Alexander III, the father of Nicholas, as part of the same investigation.