ISLAMABAD (Reuters) - A U.S. official on Friday said Washington is  deeply concerned  at the release from house arrest of a Pakistani Islamist accused of masterminding a bloody 2008 assault in the Indian city of Mumbai. Hafiz Saeed, who had been under house arrest since January, was ordered freed by a Pakistani court this week and preached on Friday at a mosque in the eastern city of Lahore. U.S. State Department spokeswoman Heather Nauert said Saeed s organization, Lashkar-e-Taiba, was responsible for the deaths of hundreds of civilians, including American citizens.  The Pakistani government should make sure that he is arrested and charged for his crimes,  Nauert said in a statement. 