Three people died and nine were injured when a Libyan fighter jet slammed into a residential area of Tobruk.
The plane, from Libya's outdated air force, went down around one kilometre from the seat of the country's elected parliament.
Video footage of the crash shows the jet flying over the city before turning upside down and plunging into buildings below.
The crash happened during a military event to honour the pilot of another warplane that crashed last week in the eastern city of Bayda.
Meanwhile, a British envoy visited Libya's parliament in a show of support against a rival assembly set up by armed groups who seized the capital Tripoli last month.
Senior officials and the elected house of representatives moved to the east of Libya when Tripoli fell to an alliance of armed factions from the western city of Misrata.
The fighting and lawlessness also prompted most countries, including Britain, to close their diplomatic missions in Libya.
The conflict is part of a wider struggle among former rebels who helped topple Moamar Gaddafi in 2011 but have now turned their weapons on each other in their fight to take power and control the country's vast oil reserves.
"We recognise the legitimacy of the Libyan parliament," said Jonathan Powell, Britain's Libya special envoy.
Western powers like Britain worry Libya will turn into a failed state that could flood Europe with migrants and become a safe haven for militant Islamists.
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