Russians have strongly supported constitutional reforms that could keep President Vladimir Putin in power until 2036, preliminary results indicate.With about 98% of ballots counted, more than 78% of voters backed the measures, the electoral commission said.
The reforms would reset Mr Putin's term limits to zero in 2024, allowing him to serve two more six-year terms.
Opposition figures denounced the vote saying he was aiming to be "president for life", a claim Mr Putin denies, BBC reported.
There was no independent scrutiny of the seven-day vote, and copies of the new constitution appeared in bookshops during the week.
Top Kremlin critic Alexei Navalny described the results as a "big lie" which did not reflect real public opinion in the country.
Preliminary results were released hours before the last polling stations closed at 18:00 GMT in the western enclave of Kaliningrad, in the vast country spanning 11 time zones.