WASHINGTON - The United States, citing the murder of Punjab Governor Salman Taseer, has voiced concern over increased extremism in Pakistan, saying political violence is a threat to the civilian government. "Well, we have been concerned about increased extremism in Pakistan for some time. It is at the heart of our Strategic Dialogue and our strategy with respect to Pakistan," US State Department spokesman Philip Crowley told reporters at his daily news briefing on Friday. He was responding to a question about the hero's treatment being given to the security guard, who shot dead the liberal-minded Taseer as the former governor spearheaded a campaign against the blasphemy law.