(Fixes day from Wednesday to Thursday)

WASHINGTON, April 9 (Reuters) - The United States said on Thursday it was troubled by reported attacks on civil society protesters in Panama for the Summit of the Americas after two Republican lawmakers blamed the violence on Castro supporters.

"We are deeply concerned by reports of attacks targeting civil society representatives in Panama for the Summit of the Americas," State Department spokeswoman Marie Harf said in a statement that did not address who was responsible. "We condemn those who use violence against peaceful protesters." (Reporting By Arshad Mohammed; Editing by Doina Chiacu)