The president of the Democratic Republic of Congo has begun his first visit to the volatile east of the country since coming to power in 2001.
Some parts of the country are still off-limits to the president
Joseph Kabila flew into the city of Kisangani, where thousands of people gave him a rapturous welcome.
Mr Kabila told them Congo was reunited after the five-year civil war.
Eastern Congo was controlled by rebels and cut off from the capital during the war and the president's visit is hugely symbolic, says the BBC's Robert Walker.
Reporting from Kisangani, our correspondent says it represents a bid by Mr Kabila to demonstrate that the authority of his transitional government now extends right across the vast country.
Thousands of cheering residents crammed into Kisangani's main square for their first chance to see President Kabila.
The president said he was sorry for what they had suffered during the country's bitter civil war, but he said that DR Congo was now united and people could once again travel from east to west.
"The process of pacification is under way and will continue until the whole country is secure and pacified," Mr Kabila said.
And - without mentioning names - he warned he would not accept "further aggression".
"Even if we say there is peace today, there are still countries that think they can return to the Congo," Mr Kabila said, without mentioning his neighbours Rwanda or Uganda by name.
The two countries supported DRC rebels in the east during much of the 1998-2003 war, which formally ended in April last year.
As he toured the city on foot, there was no doubting the warmth of the reception for the president, says our correspondent.
Mr Kabila acknowledged the huge challenges still ahead in rebuilding education and infrastructure.
But his arrival also highlights the distance still to travel before the country is properly reunified, he says.
Following last year's peace agreement, rebel leaders joined a power-sharing government.
Tens of thousands of people are still displaced.
President Kabila is still not able to visit some parts of the highly volatile east, where former rebel soldiers have refused to join the national army, and in Kisangani, local authorities have not been trusted to provide security for the visit.
The president's own soldiers have taken over the city, disarming the local police.