Interior Minister Fawzi Abd al All told a news conference it showed the new interim government was serious about tackling illegal migration to Europe, despite its limited means following months of civil war.
"This sends a strong message to the whole world that the new Libya is completely different," said Abd al All, adding that late leader Muammar Gaddafi used a threat of letting migrants sail for Europe as a way to "blackmail" Western governments, Reuters reports.
Libya under Gaddafi was a muster point for sub-Saharan Africans hoping to enter Europe illegally in search of work. Gaddafi's government secured financial and other benefits from the European Union, and Italy especially, in return for helping stem the flow of people making the short but perilous journey.
During this year's Libyan revolt, tens of thousands of migrants reached the Italian island of Lampedusa, barely 100 km (70 miles) off the African coast. Some drowned in the attempt.
"Today, tackling this problem will be different," Abd al All said through an interpreter. "The proof of that is that yesterday we were able to prevent the emigration of more than 400 or 500 emigrants. They were supposed to head for Italy."
The announcement was unexpected in a country where the central government is still weak and faces a significant challenge in disarming the many local militias that still roam the land and continue, occasionally, to clash with one other.
Shortly after the news conference, reporters found several hundred migrants corralled on the docks at Tripoli's port, where they sat in the midday sun next to a moored fishing boat.
Those who spoke briefly to Reuters said they had paid more than $1,000 each for the trip, and many believed the boat's captain had had no intention of ever making for the European coast, but had handed them straight to the Libyan authorities.
"We were deceived by these people. Libyans," said Isaac Okyere, a 27 year-old Ghanaian.
"They marched us to the Navy people," he said, adding that the boat was intercepted about 45 minutes after setting sail.
Many thousands of sub-Saharan Africans left Libya during the war when work dried up. Some also found themselves targeted by rebel forces, who accused them of fighting for Gaddafi.
Anthony Agiexeri, 32, from Nigeria, said he and others had been approached in Libya and told they would be expelled by the end of the year but could buy their way to Europe instead. He, too, said the journey was an unusually short one.
"After some time we found that the boat just drove down to this place," he said, pointing to the dock in Tripoli's main harbour where the migrants were being held.
Deputy Interior Minister Omar Hussein al-Khadrawi, who arrived at the port shortly before the migrants were loaded onto buses, denied there had been a pre-arrangement to hand them over directly to the authorities. He said: "No, it's not true."
He said the Interior Ministry had, however, received information on the vessel before it set sail, and he also added that the captain had cooperated with the operation.
"The captain was dealing with us and he knows that we know what he is going (to do)," Hussein said in English.
"It was an arrangement between us and him," he told reporters, without elaborating.
"We make progress every day, every hour, every moment," he told reporters. "We'll hopefully manage to get security under the control of the Libyan government as soon as a few weeks."
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