Once bitter rivals during the Cold War era, the US and Russia today signed two agreements to enhance their military ties, as US Defence Secretary Robert Gates said the two countries now face similar difficulties and challenges. Gates hosted his Russian counterpart Anatoliy Serdyukov at the Pentagon headquarters of the Defence Department in a high-profile visit symbolising a "reset" in the bilateral ties.The five hours of meeting between the two leaders was followed by a private riverboat dinner marking Serdyukov's maiden tour to the US and first visit to the Pentagon by a Russian defence minister in more than five years.Gates and Serdyukov signed a Memorandum of Understandings outlining the US-Russia military relationship that places defence cooperation as a cornerstone of broader relations, and notes shared threats and similar challenges.