Militants from Mend say the releases were a "dividend" from the ceasefire
Militants in Nigeria have released six crew members they seized from an oil tanker, the Sichem Peace, nearly three weeks ago.
The ship's managers, EMS, said the six, including the Russian captain, were on their way to Lagos for medical checks.
The militant group, the Movement for the Emancipation of the Niger Delta (Mend), said the release was part of a 60-day ceasefire announced last week.
The ship had already resumed commercial operations with a supplemented crew.
AFRICA HAVE YOUR SAY
Amnesty in Niger Delta will not work. Problems are not treated from its symptoms and that is what Wiwa died for
Armed men boarded the ship on 4 July. They took hostage six crew members - three Russians, two Filipinos and an Indian.
The rest of the crew were released and took the ship - which flies under the flag of Singapore - to a safe distance offshore.
The Mend statement said that the releases were a "dividend of the current ceasefire" and added that it hoped the Nigerian government would reciprocate.
The group wants the Nigerian military to withdraw from the Gbaramatu community in Delta State, and allow displaced people to return home.
The ceasefire was proposed by President Umaru Yar'Adua in May. It was accepted by Mend after the government released its leader Henry Okah on 13 July, and dropped the treason charges against him.
The violence in the Niger Delta has sharply cut Nigeria's oil production, costing it billions of dollars in lost revenue.
Mend says it is fighting for a fairer share of the wealth of the Niger Delta.
But many criminal gangs have taken advantage of the lawlessness in the area.