S&P Global Ratings and Moody's Investor Service have assigned preliminary ratings to prime residential mortgage-backed securities to be issued by Citigroup. The transaction is a securitisation of a portfolio of Australian prime residential mortgages originated by Citigroup, to be known as the Securitised Australian Mortgage Trust 2017-1."The assessment of credit risk takes into account Citigroup's underwriting standards and approval process, which are consistent with industry-wide practices, the servicing quality of Citigroup, and the support provided by the LMI policies on 2.0 per cent of the pool," S&P Global said. The A$1.5 billion Class A notes were rated AAA and Aaa by S&P and Moody's respectively. The $49 million AB notes were rated AAA by S&P, and there are also $82 million unrated notes.