The campaign headquarters of Egyptian presidential candidate Ahmed Shafiq has been attacked.
TV stations broadcast footage of a fire at the building in the Dokki district of the capital Cairo.
There are currently no reports of injuries and the BBC reports the fire was quickly put out with no signs of serious damage.
Earlier on Monday, the election commission confirmed that Mohammed Morsi of the Muslim Brotherhood and Mr Shafiq will contest a presidential run-off in June.
Mr Morsi gained 24.3% of the vote in the first round of the poll held last week and Mr Shafiq won 23.3%.
Mr Shafiq was the last prime minister to serve under Mr Mubarak.