Libya's Haftar orders forces to 'advance' on Tripoli
"The time has come. Tripoli we are coming," Haftar said in an audio message released online by his self-proclaimed Libyan National Army.
Haftar, who commands east-based LNA, described his forces' move as a "victorious march to shake the lands under the feet of the unjust."
He urged his forces to enter the city peacefully and only raise their weapons "in the face of those who seek injustice and prefer confrontation and fighting.
"Those who lay down their weapons are safe, and those who raise the white flag are safe," he added.
Unity government chief Fayez al-Sarraj has granted his air force permission to carry out strikes to repel "anyone who threatens the lives of civilians and vital facilities", local news website Al-Wasat reported.
The Tripoli-based government had said that security forces in the capital were on "high alert" and condemned the threats of an armed showdown over the capital city.
"There is no military solution to this crisis as war only brings about destruction. All sides must stop using the rhetoric of escalation and replace it with wisdom," the statement said.
Haftar's LNA announced on Wednesday it was gearing up to move on the west of the country including the capital, home to the rival unity government.
"We do not want Tripoli for power or for money, we want Tripoli for dignity, we want Tripoli for the honour of this country," LNA spokesman Ahmed Mesmari said.
Haftar's forces have emerged as a key player, opposing the government in Tripoli and backing a parallel administration in the east.
The rise in tensions came as UN boss Guterres visited Tripoli ahead of a planned conference later this month to hammer out a roadmap for delayed parliamentary and presidential elections.
"I am deeply concerned by the military movement taking place in Libya and the risk of confrontation," the visiting Guterres tweeted from the capital.
"There is no military solution" to Libya's woes, he added.