[Turkish Prime Minister Ahmet Davutoglu shakes hands with European Council President Donald Tusk after a news conference at the end of a EU-Turkey summit in Brussels]By Gabriela Baczynska and Alastair Macdonald BRUSSELS (Reuters) - The European Union aims to rehouse thousands of asylum-seekers from Greece in the coming months, officials said on Thursday as EU ministers wrestled with concerns about the legality of a new plan to force migrants back to Turkey. Dimitris Avramopoulos, the member of the executive European Commission who handles migration, told reporters at a meeting of national interior ministers that at least 6,000 people a month should be relocated to other member states under a scheme which has moved only about 900 hundred people so far. Some 35,000 people have been stranded in Greece since Austria and states on the route to Germany began closing borders, barring access to migrants hoping to follow more than a million who reached northern Europe last year.