Federal Reserve officials have agreed to sell some of their $1.1trn in mortgage backed securities (MBS) at some point, but at their meeting last month they were unable to reach a firm consensus on how soon or how aggressively to do that, according to several people familiar with the matter. Many Fed officials want to wait until after the central bank has started to tighten financial conditions by raising short term interest rates, which could be many months away, but a minority is eager to move sooner.