Six Russian sailors and an Estonian national working with a French oil and gas company and abducted by gunmen off coast of Nigeria's oil Delta have been freed, a diplomatic source told Xinhua on Thursday.

"Yes, they have been released unharmed," the source said in a brief response to Xinhua.

The source declined further comments, saying this is a very delicate and confidential matter.

The Russian Embassy in Nigeria also confirmed the release in a tweet message that the crew of Bourbon Liberty 249, hijacked by Nigerian pirates, have been released and will return home soon.