At least seven fighters loyal to Libyan National Army (LNA) forces commanded by Field Marshal Khalifa Haftar were killed overnight in a drone strike in southern Tripoli, a military source said. The eastern-based LNA had downed a drone on Sunday in Tripoli’s southern suburb of Ain Zara, it said without elaborating. In the latest turmoil since the toppling of Muammar Qaddafi in 2011, Field Marshal Haftar’s LNA has been unable to take Tripoli from the internationally recognised government despite fighting between both sides that has displaced tens of thousands of civilians. The United Nations mission in Libya said in a tweet Saturday that it was "doing its outmost with all local and foreign actors to avoid military escalation and to ensure protection of civilians". Videos circulated on social media in recent days, some by a pro-Haftar television channel, showed columns of LNA military vehicles trucking towards the south of the capital. The footage could not be independently verified. Meanwhile, Libya's national oil company has suspended operations at the country's largest oil field over the "unlawful" closure of a pipeline valve. The National Oil Corporation announced the move late on Saturday without saying who was behind the closure of the pipeline linking the field to the port of Zawiya, on the Mediterranean coast. It says the pipeline was blocked late on Friday. The Sharara oil field, which produces around 290,000 barrels a day, is controlled by forces loyal to Field Marshal Haftar. His forces launched an offensive on the capital, Tripoli, in April, where they are now locked in a stalemated battle with militias loosely aligned with a UN-recognized government.