BENGHAZI Libya (Reuters) -- Libyan Prime Minister Abdullah al-Thinni said on Sunday Qatar had sent three military planes loaded with weapons to a Tripoli airport controlled by an armed opposition group, accusing a second country of interfering in the lawless oil producer. The government had already accused Sudan of having tried to arm an Islamist-leaning group that seized Tripoli last month, forcing senior officials and the elected parliament to relocate to the east, part of a growing state of anarchy.

There was no immediate comment from Qatar, a Gulf Arab state that has backed the Muslim Brotherhood, an Islamist movement which has some ties to the group now controlling Tripoli.

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 Moammar Gadhafi.

U.S. officials have said the United Arab Emirates and Egypt, two countries worried about the spread of radical Islamists in Libya, carried out airstrikes against an armed group from the western city of Misrata conquering Tripoli last month.

"Unfortunately they [the planes] reached (TripoliMatiga airport," Thinni told UAE-based Arab TV channel Sky News. "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.

The North African country is divided, with a government and elected parliament that have relocated to Tobruk in the far east since losing control of the capital, and a rival assembly and government set up by the Misrata force.

"The Sudanese brothers are trying to interfere in Libya's affairs," Thinni said.

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.

Libya's government is unable to control dozens of former rebel groups who helped topple Gadhafi but now fight each other for power and a share of oil resources. The fluid situation in Tripoli has been worsened by a separate battle between the army and a general who has defected from it, both fighting militant Islamists.

The Islamists, including Ansar al-Sharia, made progress on Sunday in trying to take the airport, the last government bastion in the city, by moving closer, residents said.