A protest outside the Congolese Embassy in Ottawa has ended after hundreds gathered to demonstrate against the ruling president and an election they say is being hijacked.

Protesters and police both left the scene shortly after 7 p.m. after an at times tense six hours in front of the embassy, in which some demonstrators threw rocks and police responded with pepper spray. Some of the protesters vowed to return on Wednesday.

Ottawa police and the Royal Canadian Mounted Police issued a joint statement Tuesday evening saying they had arrested three people and charged one person for obstructing justice.

Police said they used a charged energy weapon — a stun gun — during one arrest and used pepper spray to disperse the crowd in an attempt to quell violent outbursts at a demonstration, which began in the early afternoon and grew to over 300 people. A protest outside Congolese embassy in Ottawa turned violent on Tuesday. Evan Dyer/CBC

The protesters had gathered outside the embassy at 18 Range Road near Laurier Avenue and chanted and sang in a mostly peaceful protest, forcing police to close Range Road between Laurier and Osgoode avenues.

But there were moments of violence as some protesters began throwing objects, including rocks, at police earlier in the afternoon.

Just after 5 p.m. about 40 to 50 riot police arrived to hold the line separating the protesters from the embassy.

RCMP Chief Superintendent Marty Cheliak said in a statement the demonstrators needed to keep the protest peaceful.

"Violent protests and violent behaviour are not tolerated," said Cheliak. "We encourage those who wish to express their Charter Rights to do so peacefully and without resorting to violence."

At its height, about 300 people crowded the area around the Congolese Embassy in Ottawa. Evan Dyer/CBC

Many of the protesters are supporters of opposition candidate Étienne Tshisekedi and say they are upset over what they are calling the "stolen election" in the Congo.

Votes are being counted in the general election, which has been marred by violence and massive logistical problems.

Preliminary results show the country's 40-year-old president Joseph Kabila in the lead.

The CBC's Evan Dyer said police told the protesters nobody is inside the embassy but the participants have said they don't believe it.

Eric Iduma, who left the scene to receive medical treatment for pepper spray, denied protesters were throwing rocks, and said he and others were only trying to access what they say is rightfully theirs.

"We ask only the police to get access to our embassy because we have a right to get inside," said Iduma. "Why they punish us to get inside?"

Moments after getting treated, Iduma, returned to the crowds to continue his protest.