Libya's Gen Khalifa Haftar, whose forces are fighting the UN-backed government in the capital Tripoli, has accepted the "popular mandate" to govern the country, he said in a televised address on Monday.

His declaration was dismissed as "the final, desperate act of a defeated man," by an adviser to Libya's UN-backed Government of National Accord (GNA).

"Haftar has once more exposed his authoritarian intentions to the world," said GNA adviser Mohammed Ali Abdallah adding, "he no longer seeks to conceal his contempt for a political solution and democracy in Libya."

Libya has been wracked by conflict since the 2011 uprising which ousted long-time leader Muammar Gaddafi.

The Libyan National Army (LNA), which is loyal to Gen Haftar, controls most of eastern Libya.

His forces have been trying to capture Tripoli and its surrounding areas - which are controlled by the GNA - for more than a year.

Speaking on Monday, Gen Haftar reportedly told TV viewers:

"We announce that the general command is answering the will of the people, despite the heavy burden and the many obligations and the size of the responsibility, and we will be subject to the people's wish."

He promised to "put in place the necessary conditions to build the permanent institutions of a civil state", according to AFP news agency.

But he did not offer details of what the new structure would look like, the Reuters news agency reports.