Mend declared a two-month ceasefire in July to allow for peace talks, but said it was now suspending negotiations with the government.
Hundreds of militant group members surrendered their weapons, mortar bombs and gunboats on Saturday.
The handover was the largest collection of weapons and ammunition since President Umaru Yar'Adua's amnesty programme began on August 6, aimed at stemming unrest in the region.
Ebikabowei Victor Ben, a former Mend leader who attended the handover ceremony on Saturday, said: "As chairman of Mend in Bayelsa state, I hand over this [flak] jacket as a proclamation that we have disarmed and stand by our word.
|Mend said they would resume their attacks on oil infrastrure in the delta next month [AFP]
"We expect the president to stand by his word and develop the Niger Delta," Ben told a crowd of hundreds of people that included former fighters, government officials and security officers.
Ben was among 25 former militant leaders who surrendered more than 500 weapons, dozens of rocket launchers and mortar bombs and 14 gunboats.
But Mend said Ben had already been replaced, and other militant group commanders in the delta's creeks had shown no such willingness to take part in the ceremony.
Attacks on pipelines and industry facilities - along with the kidnapping of oil workers - since early 2006 have cost the world's eighth-biggest oil exporter billions of dollars a year in lost revenues and added to volatility in global energy prices.
A previous attempt at disarmament under Yar'Adua's predecessor Olusegun Obasanjo in 2004 broke down as factions argued over the money paid for their weapons.
Thousands of guns were handed over, but the subsequent five years were among the most violent in the history of the Niger Delta.