The SOS Mediterranee and Doctors Without Borders (MSF) charities have relaunched migrant rescue operations off Libya, seven months after they were forced to abandon efforts using their ship Aquarius.The two groups "are back at sea with a new vessel, the Ocean Viking, to conduct search and rescue activities in the central Mediterranean", according to a statement published on Sunday."As people are still fleeing Libya on one of the most perilous sea crossings in the world, and with almost no available rescue assets present in the central Mediterranean, it has been an imperative for both SOS Mediterranee and MSF to return."Funded in partnership with MSF, the Norwegian-flagged Ocean Viking has a crew of nine, plus a search and rescue team and medical and other staff. It is expected to arrive in the central Mediterranean at the end of the month.The charities said "426 people, of which we are aware of, have died since the beginning of the year in the central Mediterranean" while attempting to "escape the escalating conflict in Libya and the deplorable conditions of Libyan detention centres".Inhuman conditionsLibya, which has been wracked by chaos since the 2011 uprising that killed longtime ruler Muammar Gaddafi, has long been a major transit route for migrants and refugees, especially from sub-Saharan Africa, trying to reach Europe.People traffickers exploited Libya's turmoil to send hundreds of thousands of migrants on dangerous journeys across the central Mediterranean, though the number of crossings dropped sharply from 2017 amid an EU-backed push to block departures.Many migrants get picked up by the Libyan coastguard, which is supported by the European Union. Thousands are being held in government-run detention centres in what human-rights groups say are often inhuman conditions.Earlier in July, one of the detention centres in the capital Tripoli was hit by an air raid, killing at least 44 people and wounding 130 others.After nearly three years of operations in which it rescued about 30,000 people, the Aquarius was forced to cease operations in December 2018 because of what the groups said was obstruction by some European countries.