The announcement comes nearly a month after Velupillai Prabhakaran, the LTTE leader, and most of his deputies, were killed by government forces in an offensive that bought the island’s 26-year civil war to an end.
According to rights groups, thousands of civilians in the north of the country were also killed in the fighting.
An estimated 250,000 Tamil refugees are currently living in military-run camps for the internally displaced that have been criticised as internment camps.
Pathmanathan, who worked as the LTTE's main international arms smuggler, said a "provisional transnational government of Tamil Eelam" was being set up.
He also said that Rudrakumaran Vishwanathan, their overseas-based legal adviser, would head a committee to decide a course of action that would be "within democratic principles".
It is not clear from where Pathmanathan, who is wanted by Interpol for his arms smuggling operations, issued the recorded message.
Al Jazeera's Tony Birtley, who has covered Sri Lanka extensively, said the new entity would probably gain a lot of support among the more than one million-strong Sri Lankan Tamil diaspora across the world.
|Some 250,000 Tamil refugees remain in what critics call internment camps [AFP]
Pointing out that the Tamil diaspora were still a tremendous source of funding for the LTTE, he said that they were "still incensed at the treatment of the internally displaced Tamils in the country and what they say is a lack of basic human rights".
"But it is difficult to see how that will translate on the ground in Sri Lanka where all LTTE structure and hierarchy have been totally destroyed leaving what some say are only 'tame and compliant' Tamils to deal with the government," our correspondent said.
"The statement by Pathmanathan speaks of a political process and makes no mention of resuming a guerrilla war. The question is will that still be the case if this transnational LTTE government is banned from the process of peace and reconciliation?"
Meanwhile, the pro-LTTE Tamilnet website called for a "democratic and inclusive" organisation to continue a separatist agenda.
"The need of the time now is the metamorphosis of the existing infrastructure into a democratic and inclusive transnational government of Eelam Tamils," Tamilnet said.
"While the government-in-exile is a conventional phenomenon that needs a host country, the transnational government is a novel experiment that has no precedence," it said, while characterising the new set-up as a "symbolic" new start for the LTTE.
The Tamil Tigers had been fighting for more than 25 years for a homeland for ethnic Tamils in the north and east of the country, saying they were marginalised by the ruling majority Sinhalese government.