Supporters of the Democratic Republic of Congo president are shocked after three senior officials were beaten up in London, a BBC correspondent says.
Leonard She Okitundu says the attack was political
The three, including President Joseph Kabila's chief of staff Leonard She Okitundu, went to hospital.
Ruling party official Placide Mbatika told the BBC his attackers were "savage" and politically motivated.
In DR Congo, campaigning has begun for the election run-off between Mr Kabila and Jean-Pierre Bemba on 29 October.
The incident took place on Wednesday night near a TV studio where the men were due to take part in a live debate on the presidential elections.
The reported attack took place close to the studios of Original Black Entertainment (OBE) TV in north London.
Mr Okitundu went to hospital with former UK ambassador Henri Nswana and Mr Mbatika, the ruling PPRD party's UK chairman, but they have since been released.
"There were six or seven guys - tall, well-built, punching me around the body," Mr Mbatika told the BBC's Network Africa programme.
He also said that some had used iron bars and had taken photos of the attack, which they had since displayed on the internet.
Joseph Kabila will face a run-off with Jean-Pierre Bemba (right)
He said they had told him he was being punished for supporting Mr Kabila, who the attackers said was not Congolese.
Mr Bemba's supporters accuse President Kabila of having Rwandan roots and selling DR Congo's mineral wealth too cheaply to foreign companies.
But Mr Bemba's spokesman told the BBC's Arnaud Zajtman in DR Congo that he condemned the attack and his party was not involved.
The three men were about to appear in a live phone-in programme for the satellite channel - which broadcasts to an Afro-Caribbean audience in the UK and abroad - when they were attacked.
A group of around 20 people reportedly set upon the three participants as they approached the studios.
OBE TV had announced two days previously that it planned to broadcast the show on Wednesday evening.
Police say they are investigating the incident.
More than 20 people were killed in clashes in the DR Congo capital, Kinshasa, between security forces loyal to Mr Bemba and Mr Kabila following the announcement of the first round results.
"I am worried for the safety of myself, the safety of my family and the safety of my country," Mr Mbatika said.