At least 18 people were wounded in two car bomb explosions that targeted a military unit in Libya's eastern coastal city of Derna, sending plumes of black smoke into the sky, a medical source and residents told Reuters early on Sunday. Residents said the car bombs targeted a military unit called Bulahati belonging to the eastern forces of the Libyan National Army (LNA) in the city centre. "We heard the first explosion, but we thought it was fireworks, then we heard the second," one resident told Reuters by telephone. "We found people around the Bulahati military unit and there was huge black smoke in the sky," another added. "We then discovered it was car bombs." Derna, once a militant bastion, is about 292 km (182 miles) distant from Libya's second city, Benghazi, and was declared to be under the complete control of Field Marshal Khalifa Haftar's LNA in June 2018. After the removal of long-time ruler Muammar Qaddafi in a Nato-backed uprising in 2011, militant groups Al Qaeda and ISIS have used the oil-rich country as a base for attacks, exploiting its chaos and lack of security. Field Marshal Haftar has pressed ahead with an offensive on Tripoli, the capital of Libya, alleging that the internationally recognised government is made up of a myriad of militias. The US and Egypt, the latter a key backer of Field MarshalHaftar, last week urged calm as clashes intensified. US Secretary of State Mike Pompeo addressed the crisis in Libya during a phone call with Egyptian Foreign Minister Sameh Shoukry, the State Department said. The two discussed "the urgent need to achieve a political solution in Libya and prevent further escalation," State Department spokeswoman Morgan Ortagus said. The fighting has left 510 dead and driven more than 75,000 people from their homes, according to World Health Organisation figures.