Tripoli - Thousands of illegal migrants who have tried to reach Europe from conflict-plagued Libya are being held in detention centres in the North African country, an official said on Monday.Most are Africans intercepted off Libyan shores or inside the country as they prepared to board boats for Europe, Mohammed Abdelsalam al-Kuwiri said.He said between 5 000 and 7 000 migrants have been held for months in 16 detention centres as Libya struggles to find planes to deport them.The centres are mainly in the Tripoli region and in Misrata east of the capital, areas controlled by the powerful Fajr Libya militia alliance.Kuwiri is in charge of combating illegal migration for the Tripoli-based government set up by Fajr Libya last August amid a power struggle with the internationally recognised administration based in the east."Up to 7 000 migrants are held in these detention centres. They are given food, mattresses and medical care," he said.Last year, before Libya plunged further into chaos with two governments vying for power, authorities were able to deport illegal migrants on flights to their native countries.But this is no longer the case, added Kuwiri, saying his government lacks the aircraft and does not have the means to deport them.In 2014, more than 25 000 illegal migrants were repatriated, compared with just 1 651 this year, he said."European countries must help us with this burden and cooperate with us to return these migrants to their homes using European planes," Kuwiri said.Stepping stoneThe United Nations says that more than 110 000 migrants transited Libya in 2014 en route to Europe.Libya, with a coastline of 1 770km, has always been a stepping stone for Africans seeking a better life in Europe, with most heading for Italy.People smugglers have exploited the chaos gripping Libya since the 2011 uprising toppled dictator Muammar Gaddafi to step up their lucrative smuggling business.On Sunday alone, Libya's coastguard intercepted five boats carrying around 500 mostly African migrants trying to reach Europe, brought them back to shore and bussed them to detention centres around Misrata.The Italian coastguard said on Sunday that 5 800 migrants were rescued at the weekend as they tried to cross the Mediterranean aboard rickety boats.On Monday, the German defence ministry said it had deployed two ships to assist a European Union migrant rescue mission beefed up last month with the aim of preventing deadly disasters at sea.In April, more than 750 people drowned in the Mediterranean's worst maritime disaster in decades. Just 26 men and two crew survived when their boat capsized.