WASHINGTON — The violence in Iraq over the last four months reflects, in part, insurgents’ response to coalition military forces going on the offense, the top American commander there said yesterday.

General David Petraeus described an ebb-and-flow of sectarian murders in Baghdad and said there has been a “stunning reversal” in the Anbar province, a former Al Qaeda stronghold west of the city where tribes have begun to help fight the terror organization.

He acknowledged, however, “real concerns” in some neighborhoods in and around Baghdad where Sunni and Shiites continue to battle.

“The fact is that as we go on the offensive, the enemy is going to respond. That is what has happened,” General Petraeus said in an interview from Baghdad. “Certainly, it is a mix. And that is what I have tried to convey in my assessments — that we are ahead in some areas and we need to do some serious work in others.”

In a required quarterly report to Congress on security, political, and economic developments in Iraq, the Pentagon last week concluded that casualties among troops and civilians have edged higher despite the American-led security push in Baghdad.

The report, covering the February-May period, also raised questions about Prime Minister al-Maliki’s ability to fulfill a January pledge to prohibit political interference in security operations and to allow no safe havens for sectarian militias. Overall, the report said it was too soon to judge whether the security crackdown was working.

Similarly, the American ambassador in Baghdad, Ryan Crocker, described the situation in Iraq as “a mixed picture, but certainly not a hopeless one.” He said there are frustrations, but also signs of progress, and cautioned about the ramifications of a precipitous withdrawal of forces.

“In terms of the political agenda, clearly we are frustrated with the slow progress that is being made on the legislative benchmarks,” Mr. Crocker said yesterday.