Egypt’s main opposition has demanded an inquiry into the referendum on the draft constitution, citing fraud.
The National Salvation Front urged the election commission to investigate the “irregularities”.
Initial unofficial results indicate a “Yes” vote for a document which President Mohammed Morsi says will safeguard democracy.
The opposition says the constitution favours Islamists, and the referendum has highlighted bitter divisions.
The result is expected to be officially announced on Monday.
If the constitution passes, elections must take place within three months. In the meantime, legislative powers would remain with Mr Morsi.