Sanaa, May 3 : Forces loyal to Yemen's government and the Houthi rebels conducted a prisoner exchange in the country's northern province of Marib, a local official said here. The official told Xinhua news agency on Sunday that 18 detainees were released as part of a prisoner exchange between the two warring sides fighting over the control of the strategic oil-rich province of Marib. The source said that the government forces and the Houthi rebels exchanged prisoners through efforts exerted by local tribal mediators. He clarified that nine prisoners were released by government troops, while nine others were released by the rebel group. Yemen's local tribal mediators have more than once succeeded in brokering prisoner exchanges between government forces and the Houthis in different areas of the war-torn Arab country. The Houthis have been beefing up the offensive in Marib since early February, which led to a slew of intense fighting between the rebels and government forces, killing hundreds on each side. The UN Office for the Coordination of Humanitarian Affairs said this week that nearly 20,000 people have been displaced by violence in the region since early February, and dozens of civilians have been killed or injured. Yemen has been mired in a civil war since late 2014 when the Iran-backed Houthi rebels seized control of several northern provinces and forced the Saudi-backed government of President Abd-Rabbu Mansour Hadi out of the capital Sanaa. The Saudi-led coalition intervened in the Yemeni military conflict in March 2015 to support Hadi's government. /IANS