Two people from the German rescue charity Sea-Eye were detained after their speedboat entered Libya's territorial waters from Tunisia without authorization, a spokesperson from the Libyan coast guard told the dpa news agency.
The 11.5 meter (roughly 40-foot) speedboat belongs to the charity Sea-Eye, which uses it in its mission to save migrants trying to cross the Mediterranean Sea to Europe.
According to Sea-Eye, the newly acquired speedboat "does quick intervention trips to the relevant area off the Libyan coast" from the Tunisian town of Zarzis.
The speedboat was operating separately from the mother ship, a refurbished, Netherlands-flagged fishing boat that cruises the waters outside Libya's 12-mile territorial zone.
According to Sea-Eye's boat tracker, the mother ship is on its way toward to the Libyan coast from Malta.
Nearly 4,000 saved
The private Sea-Eye rescue operation says it has saved nearly 4,000 people at sea in the past four months.
About 125,000 migrants, mostly from Africa, have tried to cross from Libya to Europe on rickety boats so far this year, according to Italy's Interior Ministry.
A European Union anti-smuggling mission, Italy's navy and coast guard, and vessels run by humanitarian groups aid in migrant rescue operations in the Mediterranean.