Militias in Nigeria's oil-rich Delta region have agreed to stop fighting.
The Nigerian army is maintaining its heavy presence in the region
The agreement between the Itsekiri and Ijaw ethnic groups is supposed to end seven years of warring, which has badly disrupted oil production in the area.
The deal reached in the town of Warri came shortly after local authorities sent the army into the region's swamps and creeks to arrest the militiamen.
Fighting in the oil-rich region flared in March forcing several multi-national oil companies to halt operations.
In the latest major incident, seven oil workers, including two Americans, were killed by militiamen last April.
The fighting has left hundreds dead and thousands homeless, while damaging Nigeria's export trade and oil industry.
Chiefs from both the Ijaw and Itsekiri tribes met face to face for the first time in Warri to declare the ceasefire and begin peace talks.
"The only solution to our problems is at a round table, not behind the barrel of a gun," Dan Reyenieju, leader of an Itsekiri delegation said.
His views were echoed by the Ijaw leader Kingsley Otuaro, who said: "This is a great day, this is definitely the solution to our problems."
"We have disseminated the information to our guys in the villages that we do not want, for any reason, to hear any gunshots," Mr Otuaro added.
"The information has been passed on and as we speak there are men on the ground to enforce all that we say here."
Correspondents say that past attempts to achieve peace have failed because they were brokered by local politicians and ethnic leaders who in practice had very little influence over the militia on the ground.
They also say that the new willingness to put violence aside now is due in no small part to pressure from the Nigerian army, which moved into the area following the April attacks on oil workers.
They moved in, razing shanty towns and arresting suspected guerrilla leaders.
The meeting began with prayers were said for all those killed in the clashes
There was a strong army presence at the ceasefire meeting, with gunboats patrolling the muddy waters of the surrounding river and swamp areas.
The military has welcomed the ceasefire pledge, but has warned that their mission is still not done, and will continue until the delta region is secure.
"The situation changes every day. At the moment I cannot guarantee your safety on the waterways," said Brigadier-General Elias Zamani, commander of the peace-enforcement mission.
Nigeria is Africa's biggest oil exporter, churning out more than 2.5m barrels per day.
But the years of violence have proven extremely costly. At the height of the fighting 40% of Nigeria's oil exports were stopped as foreign firms withdrew their staff.