Navi Pillay told a closed-door session of the Security Council on the latest development on Syria that 14,000 people are believed to have been prisoned and 12,400 fled to neighbouring countries.
Syria’s ambassador to the UN rejected these figures, saying Ms Pillay was “not objective and “not fair”.
Opposition claimed at least 20 people died in clashes on Monday.
On Monday, local election began despite ongoing bloody violence in the country. Opposition has already boycotted the elections and announced a general strike.
Authorities have claimed the elections would be freer than in previous years. They also said the vote had been freer than in previous years, but the opposition had called for a boycott and launched a general strike.
There are reports that show there are few signs of election and there is no-one on polling booths to cast vote. But state news agency told people had flocked to polling booths.
Syria has denied to international election monitors as well.
Reporters also adds that Syria’s third largest city, Homs is presenting the view of a war hit area, with gun- battles occurring everyday between heavily armed security forces and lightly armed protesters.
The uprising in Syria is a part of broader popular protest movement that led to the toppling of heads in Egypt, Libya, Tunisia and Yemen.