The raids took place Friday in the western town of Gargaresh as part of what authorities described as a security campaign against illegal migration and drug trafficking. The Interior Ministry, which led the crackdown, made no mention of any traffickers or smugglers being arrested.
Officials said Friday that 500 illegal migrants had been detained but on Saturday reported that number had reached 4,000.
Gargaresh, a known hub for migrants and refugees, is about 12 kilometers (7.5 miles) west of Tripoli, the Libyan capital. The town has seen several waves of raids on migrants over the years, but the latest one was described by activists as the fiercest so far.
Since the 2011 NATO-backed uprising that ousted and killed longtime dictator Muammar Qaddafi, Libya has emerged as the dominant transit point for migrants fleeing war and poverty in Africa and the Middle East, hoping for a better life in Europe. Human traffickers have benefited from the chaos in the oil-rich nation and smuggled migrants through the country’s lengthy border with six nations. They then pack desperate migrants into ill-equipped rubber boats in risky voyages through the perilous Central Mediterranean Sea route.