Libyan Prime Minister Abdullah al-Thinni has alleged that Qatar is responsible for sending three military planes loaded with weapons to a Tripoli airport controlled by an armed opposition group.
The government had already accused Sudan of having tried to arm a group which seized Tripoli last month, forcing senior officials and the elected parliament to relocate to the east.
There was no immediate comment from Qatari officials.
Also on Monday, Libyan forces of retired General Haftar in Benghazi said that they have closed the city's port to stop arms supplies, according to the Reuters news agency.
Analysts say Libya is turning into a conflict zone for competing regional powers, as the country faces the prospect of becoming a failed state or even civil war three years after the ousting of Muammar Gaddafi.
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US officials have said that the United Arab Emirates and Egypt carried out air strikes against an armed group from the western city of Misrata conquering Tripoli last month.
"Unfortunately they [the planes] reached [Tripoli] Matiga airport," Thinni told UAE-based Sky News Arabia.
"We will consider ... breaking off relations if this interference into Libya's internal affairs continued."
"We confirm that we have official reports that these war planes carried weapons and ammunition," he said. "What does Qatar want to give to the Libyan people?"
Thinni also repeated accusations against Sudan, saying Khartoum had tried sending a military plane loaded with ammunition to Matiga, an airport controlled by the Misrata forces.
Sudan has confirmed it had sent a plane to the Libyan airport of Kufra but says it was only carrying equipment for a joint Libyan-Sudanese border force.
Thinni said the Qatari military planes had arrived in Matiga before the Sudanese plane was stopped by Libyan forces in Kufra, a desert town near the Sudanese border.