The United Nations agency that distributes food to a majority of Gaza’s refugees said Friday that it was suspending imports of goods because Hamas, the militant group that controls Gaza, had twice stolen aid from it. The agency said that it would not import any more until the stolen goods were returned and assurances were given that the theft would not recur. A Hamas spokesman attributed the most recent incident, on Thursday night, to a misunderstanding among truck drivers, and said that those who stole an earlier load from a United Nations distribution site were not part of Hamas. He said that Hamas and United Nations officials were meeting and that he expected the problem to be cleared up quickly.