In an email to the media, Mend said: "The plan involved paying 70 million naira [$545,000] to those supposed to be guarding the hostages for the hostages to be guided to a point where a boat was to be stationed to take them out of the creeks.
"A middleman brought 70 million naira to one of our camps where the attempt was immediately reported. Needless to say, the money has been confiscated and will be put to better use."
A Nigerian spokesman for Agip, a unit of Italy's Eni, has declined to comment.
Mend said such plans endangered the lives of the hostages as their guards had orders to shoot them if any attempt was made to release them without authorisation.
Attacks on oil facilities and abductions of foreign oil workers have plagued the Niger Delta for years, but the violence worsened last year and is expected to increase further in the build-up to Nigeria's general elections in April.
Nigeria, an Opec member and the world's eighth-biggest exporter of crude, receives all of its oil from the Niger Delta. But the vast, impoverished region has long been neglected by the central and local governments.
Since the abductions on December 7, Mend has detonated three car bombs in the delta's main city, Port Harcourt, prompting oil majors Shell and Total to pull out hundreds of relatives of their expatriate staff.
Roberto Dieghi, one of the Italian hostages, is suffering from various ailments and doctors from the humanitarian organisation Medecins Sans Frontieres (MSF) will be allowed to visit him, according to a statement issued by Mend on Tuesday.
The MSF head of mission in Port Harcourt said that his organisation had not been contacted by anyone from Mend.