* Gov't dismisses army officer's video call for "rescue"
* Political tensions high over future of interim Congress
* Rival militias still more powerful than nascent army (Adds details on protests)
By Ghaith Shennib
TRIPOLI, Feb 14 (Reuters) - Libyan Prime Minister Ali Zeidan said on Friday the government was safe and security under control, dismissing a statement by a senior army official calling for the parliament to be suspended and the armed forces to "rescue" the country.
Major General Khalifa Haftar, a leading figure in the 2011 revolution against Muammar Gaddafi, called in a video statement for a presidential committee to govern until new elections in what he described as a "road map" rather than a coup bid.
Government officials quickly brushed off Haftar's video, in which the grey-haired officer appeared in military uniform, as the work of a retired soldier with no backing within Libya's armed forces.
But the confusion it provoked was a reminder of the fragility of Libya's transition to democracy with its interim government and General National Congress or GNC parliament paralysed by infighting among rival factions.
Nearly three years after Gaddafi's fall, Libya's government is fragile, its constitution undrafted and its armed forces unable to impose their authority on the brigades of former revolutionary fighters who refuse to disarm.
"Libya is stable. The GNC is doing its work and so is the government. The army is in its headquarters and Khalifa Haftar has no authority," Prime Minister Ali Zeidan told Reuters. "No military units have moved to touch any institutions."
He said legal proceedings under military law would be taken against Haftar for his statement.
Tripoli appeared calm and there were no troop movements or activity outside the parliament, the prime minister's office or any ministries.
It was not clear even how much influence Haftar has within the small, nascent army in a country where the brigades of militia groups and former rebels are more powerful.
"The national command of the Libyan army is declaring a movement for the new road map," Haftar said, adding the armed forces were calling for Libya to be "rescued" from its upheaval.
Later several thousand protesters gathered in Tripoli, Benghazi and al Bayda, to demonstrate peacefully against the GNC parliament. But their reactions to Haftar ranged from applause for his message to outright rejection.
"We are protesting against the GNC and the government peacefully, it is not related to what Hafter said... We still have hope in democracy," said activist Rahaf Salim in Tripoli.
Libya's army barely exists, with most of its soldiers still in training or drawn from the ranks of former rebels who are often more loyal to their own regions, their commanders or their tribes than a national force.
Haftar was once a Gaddafi ally, but broke with the autocratic leader over the war with Chad in the 1980s. He later sought exile in the United States, but returned to become a commander of forces in the 2011 revolution.
Much of Libya's current political tension centres on the General National Congress, which is deeply split between the nationalist National Forces Alliance party and the Islamists of the Justice and Construction Party, which is tied to the Muslim Brotherhood, and the Al Wafaa movement.
Since its election in 2012, the GNC has become increasingly unpopular with Libyans who see it has made little progress in the transition to democracy.
But tensions have increased over its future after its initial mandate ran out on Feb. 7. Its members agreed to extend their term in office to allow a special committee the stability to draft the constitution.
Rival political factions and militia groups have competing views on how the country should continue, with some calling for early elections and others supporting the extension of the parliament's mandate.
Libyans will vote on Feb. 20 for the special assembly to draft the constitution over the next few months, that if successful would be a rare bright spot in a transition so far marked by instability and violence. (Additional reporting by Feras Bosalum and Hani Amara in Tripoli; Writing by Patrick Markey; Editing by Gareth Jones)