Security has been stepped up in the border town of Bukavu after Rwanda and Burundi said they could send troops into Democratic Republic of Congo.
June's fighting in Bukavu led thousands of Tutsis to flee
"People are scared," local radio station director Kizito Mushizi told the BBC.
Rwanda and Burundi were responding to the massacre of more than 150 Congolese Tutsi refugees in Burundi.
Some of the massacre survivors have been tear-gassed by Burundi soldiers after protesting in the capital.
Some 200 people were demonstrating outside the DR Congo embassy and UN offices in Bujumbura and tore up the Congolese flag.
Burundi has also issued international arrest warrants for Agathon Rwasa and Pasteur Habimana, the leader and spokesman of the Hutu rebel National Liberation Forces (FNL) which claimed responsibility for the massacre.
Regional leaders are discussing the killing and the Burundi peace process at a summit in Tanzania.
President Joseph Kabila of DR Congo and his Burundian counterpart Domitien Ndayizeye have held bilateral talks to defuse tensions, officials say.
Both Rwandan and Burundian troops fought in DR Congo's five-year war, which officially ended in 2002, after the death of some three million people.
DR Congo-based Hutu rebels are still fighting Tutsi-dominated armies in both Burundi and Rwanda.
The BBC's Arnaud Zajtman in Bukavu says that there are checkpoints everywhere and almost all cars are being searched.
The refugees fled DR Congo after fighting in Bukavu in June between Tutsi rebels and the DR Congo army.
DR Congo's Defence Minister Jean-Pierre Ondekane said that invading his country would not solve the problem "because these rebels are in all three countries," reports the AP news agency.
But South Africa's leader has said that the massacre would not derail Burundi's peace process.
Thabo Mbeki was speaking ahead of the summit in Dar es Salaam, which was originally called to discuss a deal brokered by South Africa to share power between ethnic Hutu and Tutsi groups.
Rwanda and Burundi say that armed groups based in DR Congo took part in the massacre, even though the FNL has admitted responsibility.
The African Union has urged member states to impose a travel ban on FNL leaders and South Africa has said it should be declared a terrorist group.
Mr Mbeki told South African radio that he hoped Burundi could still hold elections in October, as set out in a previous transitional power-sharing agreement.
Mr Ndayizeye has said the polls should be postponed until former rebels from the Forces for the Defence of Democracy (FDD) disarmed.
The eight African leaders are expected to ratify a deal, which sets aside 40% of seats in parliament for the minority Tutsis, who make up 15% of the population.
Tutsis have long dominated Burundi but following the 1994 genocide in neighbouring Rwanda, they fear reprisals if they give up power and the main Tutsi party, Uprona, has rejected the deal.
The FDD has joined the Burundi government but the FNL has refused to take part in the peace process.
The United Nations has said it had suspended negotiations with the FNL.
Some 300,000 people have died in 11 years of conflict in Burundi but until this massacre, the scale of violence had reduced in recent months.