By Ross Kerber (Reuters) -Top asset manager BlackRock on Wednesday pushed back against pressure from U.S. Republican and Democratic officials, saying both sides have injected politics into the running of retirement assets and it only seeks to fulfill its fiduciary duties to clients. The message isn't new but it came in an unusual memo the company sent to 43 state treasurers, auditors and other officials of both major political parties, seen by Reuters. In late July, 26 Republicans signed on to a letter questioning if BlackRock paid too much attention to matters like climate change, while this month 17 Democrats responded with their own note describing climate change among the "unmanaged risks" that deserve more investor focus. BlackRock's head of state and local government affairs, S. Jane Moffat, told all of them that their letters "continue a concerning trend by both parties of politicizing the management of public pension funds."