Libya's UN-recognized Government of National Accord (GNA) on Sunday denounced Egypt's warning of military intervention in Libya, labeling it a "declaration of war."

"This is a hostile act, direct interference and amounts to a declaration of war," the GNA said in a statement.

On Saturday, Egyptian President Abdel Fattah al-Sisi warned that if pro-GNA forces advanced on the strategic city of Sirte – some 450 kilometers (280 miles) east of Tripoli – it could provoke a "direct" intervention by Cairo.

For the Libyan state, "interference in its internal affairs, attacks on its sovereignty, whether by declarations ... like those of the Egyptian president or by support for putschists, militias and mercenaries, is unacceptable," the GNA said.

It said it was open to "all impartial mediation ... under the aegis of the UN" but rejected "unilateral or extrajudicial initiatives."

Forces loyal to the GNA were reported to have driven strongman Khalifa Haftar's Libyan National Army (LNA) from large swaths of territory in the west of the war-torn country and also strategic towns near Tripoli.

At present, GNA forces have launched a campaign, moving eastward, to capture Sirte from the LNA.

Oil-rich Libya has been torn by violence, drawing in tribal militias, jihadists and mercenaries since the 2011 toppling and killing of Muammar Gaddafi.

Since 2015, a power struggle has pitted the Tripoli-based GNA against strongman Khalifa Haftar, who claims legitimacy from an eastern-based elected parliament.

Haftar has been trying unsuccessfully to seize the capital since April 2019, with support from Egypt, Russia and the United Arab Emirates.

Since the start of June, increased Turkish support has enabled pro-GNA forces to take control of northwest Libya, ending Haftar's assault on Tripoli.

The GNA advance is now halted outside the coastal city of Sirte, a strategic access point to Libya's key oil fields which remains under Haftar's control.

Sirte and Al-Jufra to the south represents a "red line," Sisi said in a television broadcast on Saturday, citing the need to protect Egypt's porous border.

If this line is crossed, Egyptian forces will directly intervene in Libya, Sisi said.

"All of Libya is a red line," the GNA responded. "Whatever the dispute between Libyans, we will not allow our people to be insulted or threatened."

But the speaker of Libya's eastern-based parliament Aguila Saleh defended Sisi's declaration, saying in a Sunday statement that the Egyptian president was "responding to our appeal to the Egyptian parliament" last January in which Saleh called for Egyptian intervention in Libya.

And on Sunday the Jordanian foreign ministry issued a statement saying Amman supports Cairo's decision after discussing the Libya conflict with his Egyptian counterpart over the phone.

(With input from agencies)