A fire has broken out at the party headquarters of Democratic Republic of Congo opposition leader Jean-Pierre Bemba in the capital, Kinshasa.
Joseph Kabila (l) faces Jean-Pierre Bemba (r) in October's run-off
Plumes of smoke billowed out from the building, which houses Mr Bemba's TV stations. A crowd stoned fire fighters and UN troops when they arrived.
One of Mr Bemba's aides blamed people close to President Joseph Kabila - charges denies by the ruling party.
Mr Bemba is to contest an election run-off against Mr Kabila next month.
There are reports that a senior TV executive was seriously burned but it is not clear what started the blaze.
Crowds of Mr Bemba's supporters gathered outside the building.
"Things are going to get hot today! Those who think Bemba will die are wrong," they chanted.
Fidel Balala, one of Mr Bemba's senior aides accused "Kabila and his group" of being behind the fire.
"It is unfair. They are once more showing that they are not real democrats."
But Vital Kamerhe, Secretary General of the ruling PPRD party rejected the accusation.
"It is absolutely wrong. We have nothing to do with this. Bemba's people pretend to be the fire brigade while they are in fact the arsonists."
The announcement of the first round results led to three days of gun battles in Kinshasa between the two men's security forces, which left at least 23 people dead.
The second round will conclude the country's first democratic polls since independence in 1960.
Mr Bemba, a former rebel leader, came second in the first round, with 20% of the vote, compared to 45% for Mr Kabila.