Having shunned US mortgage-related assets for 1.5 years, foreign investors are returning to the market now the US government has a key stake. Overseas demand is mounting given the US Federal Reserve today owns over 20% of agency mortgage assets after a 15-month buying spree to lower home loan rates and revive the US housing market. Added to that, the US Treasury has pledged unlimited credit access to mortgage giants Fannie Mae and Freddie Mac for three years.