The leader of Congo's former rebel group, the Ninjas, has not returned to Brazzaville as expected, after army helicopters swooped down on his men.
The army helicopters were used during the five-year war
BBC correspondent John James says the young men lining the streets waiting to enter the city to welcome Pasteur Ntumi responded by brandishing machine-guns.
He did not hear shots fired but says this is not good for the peace process.
Mr Ntumi had been due to take a place in the government, as a junior minister responsible for peace and disarmament.
Before the military attack helicopters approached the Ninja group, Mr Ntumi's return had already been delayed.
The former rebels were not happy with the presence of armed police on the bridge over the Djoue River on the western edge of the capital.
Our correspondent says this appeared contrary to the security arrangements for the day.
The Ninjas brandished their weapons, which had been hidden
Hours of negotiations followed before the dramatic arrival of the helicopters sent people running for cover, while the former fighters took out their weapons, including rocket launchers, which had been hidden.
Government spokesman Alain Akouala, however, blamed the confusion on Mr Ntumi, who he said had tried to bring 300 armed bodyguards into the city - far more than the 30 which had been agreed.
Mr Akouala said the helicopter has just been on a "routine flight".
These helicopters were one of the major weapons in the government's five-year war with the Ninjas, which formally ended with a peace deal in 2003.
Our correspondent says the government was also concerned by the presence of thousands of Ninjas and supporters of the semi-religious group, who had lined the capital's streets to welcome their leader.
After his return to Brazzaville for the first time in 10 years was called off, they streamed out of the city.
Pasteur Ntumi transformed his rebel movement into a political party at the beginning of the year and signed a peace agreement in April giving him a ministerial post.
The party contested parliamentary elections in June and August, but without success.
Our correspondent says it is likely to be a while before Pasteur Ntumi again thinks of leaving his forest hideout in the western Pool region.